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 $43.39   12.516%   $48.8207   $48.82   $48.80   $48.80  
  Purchase #2 $201.93   12.357%   $226.8825   $226.88   $226.90   $226.90  
  Purchase #3 $63.72   10.496%   $70.4081   $70.41   $70.40   $70.40  
  Purchase #4 $167.34   4.318%   $174.5657   $174.57   $174.55   $174.60  
  Purchase #5 $19.69   4.517%   $20.5794   $20.58   $20.60   $20.60  
  Purchase #6 $202.78   4.414%   $211.7307   $211.73   $211.75   $211.70  
  Purchase #7 $170.66   10.535%   $188.639   $188.64   $188.65   $188.60  
  7 purchase totals = $869.51       $941.6261   $941.63   $941.65   $941.60