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 $227.58   11.396%   $253.515   $253.52   $253.50   $253.50  
  Purchase #2 $35.49   8.342%   $38.4506   $38.45   $38.45   $38.50  
  Purchase #3 $61.94   9.498%   $67.8231   $67.82   $67.80   $67.80  
  Purchase #4 $47.60   12.126%   $53.372   $53.37   $53.35   $53.40  
  Purchase #5 $155.73   8.499%   $168.9655   $168.97   $168.95   $169.00  
  Purchase #6 $173.51   8.628%   $188.4804   $188.48   $188.50   $188.50  
  Purchase #7 $201.77   7.360%   $216.6203   $216.62   $216.60   $216.60  
  7 purchase totals = $903.62       $987.2269   $987.23   $987.15   $987.30