Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $178.89   12.363%   $201.0062   $201.01   $201.00   $201.00  
  Purchase #2 $214.53   12.203%   $240.7091   $240.71   $240.70   $240.70  
  Purchase #3 $101.90   10.266%   $112.3611   $112.36   $112.35   $112.40  
  Purchase #4 $46.34   4.247%   $48.3081   $48.31   $48.30   $48.30  
  Purchase #5 $166.91   4.537%   $174.4827   $174.48   $174.50   $174.50  
  Purchase #6 $134.51   10.586%   $148.7492   $148.75   $148.75   $148.70  
  Purchase #7 $174.93   10.632%   $193.5286   $193.53   $193.55   $193.50  
  7 purchase totals = $1,018.01       $1,119.1450   $1,119.15   $1,119.15   $1,119.10