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 $75.28   12.352%   $84.5786   $84.58   $84.60   $84.60  
  Purchase #2 $194.33   3.426%   $200.9877   $200.99   $201.00   $201.00  
  Purchase #3 $180.42   11.775%   $201.6645   $201.66   $201.65   $201.70  
  Purchase #4 $35.81   6.494%   $38.1355   $38.14   $38.15   $38.10  
  Purchase #5 $125.53   10.271%   $138.4232   $138.42   $138.40   $138.40  
  Purchase #6 $125.64   5.386%   $132.407   $132.41   $132.40   $132.40  
  Purchase #7 $56.90   5.240%   $59.8816   $59.88   $59.90   $59.90  
  7 purchase totals = $793.91       $856.0781   $856.08   $856.10   $856.10