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 $51.65   11.843%   $57.7669   $57.77   $57.75   $57.80  
  Purchase #2 $241.65   7.587%   $259.984   $259.98   $260.00   $260.00  
  Purchase #3 $100.66   3.581%   $104.2646   $104.26   $104.25   $104.30  
  Purchase #4 $110.57   11.495%   $123.28   $123.28   $123.30   $123.30  
  Purchase #5 $90.87   13.289%   $102.9457   $102.95   $102.95   $102.90  
  Purchase #6 $14.74   13.797%   $16.7737   $16.77   $16.75   $16.80  
  Purchase #7 $192.30   7.226%   $206.1956   $206.20   $206.20   $206.20  
  7 purchase totals = $802.44       $871.2105   $871.21   $871.20   $871.30