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 $30.78   6.426%   $32.7579   $32.76   $32.75   $32.80  
  Purchase #2 $110.41   13.233%   $125.0206   $125.02   $125.00   $125.00  
  Purchase #3 $187.54   8.118%   $202.7645   $202.76   $202.75   $202.80  
  Purchase #4 $89.27   5.683%   $94.3432   $94.34   $94.35   $94.30  
  Purchase #5 $93.68   5.782%   $99.0966   $99.10   $99.10   $99.10  
  Purchase #6 $172.55   9.213%   $188.447   $188.45   $188.45   $188.40  
  Purchase #7 $218.45   6.361%   $232.3456   $232.35   $232.35   $232.30  
  7 purchase totals = $902.68       $974.7754   $974.78   $974.75   $974.70