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 $212.81   10.253%   $234.6294   $234.63   $234.65   $234.60  
  Purchase #2 $226.74   10.195%   $249.8561   $249.86   $249.85   $249.90  
  Purchase #3 $20.86   12.269%   $23.4193   $23.42   $23.40   $23.40  
  Purchase #4 $11.67   9.830%   $12.8172   $12.82   $12.80   $12.80  
  Purchase #5 $188.90   8.442%   $204.8469   $204.85   $204.85   $204.80  
  Purchase #6 $51.58   5.324%   $54.3261   $54.33   $54.35   $54.30  
  Purchase #7 $11.79   13.467%   $13.3778   $13.38   $13.40   $13.40  
  7 purchase totals = $724.35       $793.2728   $793.29   $793.30   $793.20