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 $235.67   12.433%   $264.9709   $264.97   $264.95   $265.00  
  Purchase #2 $191.71   13.496%   $217.5832   $217.58   $217.60   $217.60  
  Purchase #3 $236.76   12.148%   $265.5216   $265.52   $265.50   $265.50  
  Purchase #4 $134.91   10.427%   $148.9771   $148.98   $149.00   $149.00  
  Purchase #5 $49.73   11.263%   $55.3311   $55.33   $55.35   $55.30  
  Purchase #6 $46.78   9.175%   $51.0721   $51.07   $51.05   $51.10  
  Purchase #7 $39.46   12.771%   $44.4994   $44.50   $44.50   $44.50  
  7 purchase totals = $935.02       $1,047.9554   $1,047.95   $1,047.95   $1,048.00