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 $54.88   10.123%   $60.4355   $60.44   $60.45   $60.40  
  Purchase #2 $71.89   4.865%   $75.3874   $75.39   $75.40   $75.40  
  Purchase #3 $190.69   6.169%   $202.4537   $202.45   $202.45   $202.50  
  Purchase #4 $25.26   7.447%   $27.1411   $27.14   $27.15   $27.10  
  Purchase #5 $227.82   7.328%   $244.5146   $244.51   $244.50   $244.50  
  Purchase #6 $164.97   13.828%   $187.7821   $187.78   $187.80   $187.80  
  Purchase #7 $244.88   4.230%   $255.2384   $255.24   $255.25   $255.20  
  7 purchase totals = $980.39       $1,052.9528   $1,052.95   $1,053.00   $1,052.90