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 $45.82   5.350%   $48.2714   $48.27   $48.25   $48.30  
  Purchase #2 $140.77   8.505%   $152.7425   $152.74   $152.75   $152.70  
  Purchase #3 $248.44   12.717%   $280.0341   $280.03   $280.05   $280.00  
  Purchase #4 $167.68   11.809%   $187.4813   $187.48   $187.50   $187.50  
  Purchase #5 $86.87   13.842%   $98.8945   $98.89   $98.90   $98.90  
  Purchase #6 $130.39   11.213%   $145.0106   $145.01   $145.00   $145.00  
  Purchase #7 $60.91   13.299%   $69.0104   $69.01   $69.00   $69.00  
  7 purchase totals = $880.88       $981.4448   $981.43   $981.45   $981.40