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 $46.27   8.610%   $50.2538   $50.25   $50.25   $50.30  
  Purchase #2 $67.44   11.202%   $74.9946   $74.99   $75.00   $75.00  
  Purchase #3 $24.35   8.831%   $26.5003   $26.50   $26.50   $26.50  
  Purchase #4 $98.39   12.725%   $110.9101   $110.91   $110.90   $110.90  
  Purchase #5 $74.26   12.805%   $83.769   $83.77   $83.75   $83.80  
  Purchase #6 $210.41   13.563%   $238.9479   $238.95   $238.95   $238.90  
  Purchase #7 $236.48   13.717%   $268.918   $268.92   $268.90   $268.90  
  7 purchase totals = $757.60       $854.2937   $854.29   $854.25   $854.30