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 $143.34   13.411%   $162.5633   $162.56   $162.55   $162.60  
  Purchase #2 $203.87   10.554%   $225.3864   $225.39   $225.40   $225.40  
  Purchase #3 $54.72   7.762%   $58.9674   $58.97   $58.95   $59.00  
  Purchase #4 $210.71   10.447%   $232.7229   $232.72   $232.70   $232.70  
  Purchase #5 $176.27   11.509%   $196.5569   $196.56   $196.55   $196.60  
  Purchase #6 $95.34   12.177%   $106.9496   $106.95   $106.95   $106.90  
  Purchase #7 $117.86   6.689%   $125.7437   $125.74   $125.75   $125.70  
  7 purchase totals = $1,002.11       $1,108.8902   $1,108.89   $1,108.85   $1,108.90