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 $106.87   10.762%   $118.3713   $118.37   $118.35   $118.40  
  Purchase #2 $175.65   4.234%   $183.087   $183.09   $183.10   $183.10  
  Purchase #3 $89.51   4.599%   $93.6266   $93.63   $93.65   $93.60  
  Purchase #4 $45.55   13.731%   $51.8045   $51.80   $51.80   $51.80  
  Purchase #5 $190.91   3.543%   $197.6739   $197.67   $197.65   $197.70  
  Purchase #6 $143.30   6.148%   $152.1101   $152.11   $152.10   $152.10  
  Purchase #7 $122.63   5.479%   $129.3489   $129.35   $129.35   $129.30  
  7 purchase totals = $874.42       $926.0223   $926.02   $926.00   $926.00