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 $49.51   9.390%   $54.159   $54.16   $54.15   $54.20  
  Purchase #2 $10.26   12.631%   $11.5559   $11.56   $11.55   $11.60  
  Purchase #3 $85.79   6.356%   $91.2428   $91.24   $91.25   $91.20  
  Purchase #4 $210.93   11.441%   $235.0625   $235.06   $235.05   $235.10  
  Purchase #5 $234.61   4.672%   $245.571   $245.57   $245.55   $245.60  
  Purchase #6 $43.73   6.379%   $46.5195   $46.52   $46.50   $46.50  
  Purchase #7 $105.26   10.497%   $116.3091   $116.31   $116.30   $116.30  
  7 purchase totals = $740.09       $800.4198   $800.42   $800.35   $800.50