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 $63.28   3.319%   $65.3803   $65.38   $65.40   $65.40  
  Purchase #2 $108.85   8.179%   $117.7528   $117.75   $117.75   $117.80  
  Purchase #3 $207.26   9.752%   $227.472   $227.47   $227.45   $227.50  
  Purchase #4 $224.41   5.156%   $235.9806   $235.98   $236.00   $236.00  
  Purchase #5 $44.46   12.594%   $50.0593   $50.06   $50.05   $50.10  
  Purchase #6 $193.62   6.393%   $205.9981   $206.00   $206.00   $206.00  
  Purchase #7 $37.83   5.692%   $39.9833   $39.98   $40.00   $40.00  
  7 purchase totals = $879.71       $942.6264   $942.62   $942.65   $942.80