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 $237.51   6.816%   $253.6987   $253.70   $253.70   $253.70  
  Purchase #2 $103.88   13.871%   $118.2892   $118.29   $118.30   $118.30  
  Purchase #3 $148.26   8.210%   $160.4321   $160.43   $160.45   $160.40  
  Purchase #4 $160.39   11.789%   $179.2984   $179.30   $179.30   $179.30  
  Purchase #5 $202.80   5.404%   $213.7593   $213.76   $213.75   $213.80  
  Purchase #6 $207.26   3.518%   $214.5514   $214.55   $214.55   $214.60  
  Purchase #7 $69.99   3.869%   $72.6979   $72.70   $72.70   $72.70  
  7 purchase totals = $1,130.09       $1,212.7270   $1,212.73   $1,212.75   $1,212.80