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 $196.58   5.842%   $208.0642   $208.06   $208.05   $208.10  
  Purchase #2 $125.42   6.290%   $133.3089   $133.31   $133.30   $133.30  
  Purchase #3 $50.73   8.731%   $55.1592   $55.16   $55.15   $55.20  
  Purchase #4 $190.31   11.462%   $212.1233   $212.12   $212.10   $212.10  
  Purchase #5 $237.94   3.609%   $246.5273   $246.53   $246.55   $246.50  
  Purchase #6 $117.77   6.496%   $125.4203   $125.42   $125.40   $125.40  
  Purchase #7 $143.34   5.341%   $150.9958   $151.00   $151.00   $151.00  
  7 purchase totals = $1,062.09       $1,131.5990   $1,131.60   $1,131.55   $1,131.60