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 $200.97   13.453%   $228.0065   $228.01   $228.00   $228.00  
  Purchase #2 $206.82   12.819%   $233.3323   $233.33   $233.35   $233.30  
  Purchase #3 $94.87   5.193%   $99.7966   $99.80   $99.80   $99.80  
  Purchase #4 $222.28   4.788%   $232.9228   $232.92   $232.90   $232.90  
  Purchase #5 $143.54   6.539%   $152.9261   $152.93   $152.95   $152.90  
  Purchase #6 $229.46   3.347%   $237.14   $237.14   $237.15   $237.10  
  Purchase #7 $51.40   4.713%   $53.8225   $53.82   $53.80   $53.80  
  7 purchase totals = $1,149.34       $1,237.9468   $1,237.95   $1,237.95   $1,237.80