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 $31.92   11.516%   $35.5959   $35.60   $35.60   $35.60  
  Purchase #2 $62.64   4.195%   $65.2677   $65.27   $65.25   $65.30  
  Purchase #3 $119.55   8.742%   $130.0011   $130.00   $130.00   $130.00  
  Purchase #4 $48.56   6.320%   $51.629   $51.63   $51.65   $51.60  
  Purchase #5 $25.84   13.866%   $29.423   $29.42   $29.40   $29.40  
  Purchase #6 $71.67   7.357%   $76.9428   $76.94   $76.95   $76.90  
  Purchase #7 $205.41   8.817%   $223.521   $223.52   $223.50   $223.50  
  7 purchase totals = $565.59       $612.3805   $612.38   $612.35   $612.30