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 $28.94   12.389%   $32.5254   $32.53   $32.55   $32.50  
  Purchase #2 $134.36   7.671%   $144.6668   $144.67   $144.65   $144.70  
  Purchase #3 $205.80   8.763%   $223.8343   $223.83   $223.85   $223.80  
  Purchase #4 $23.45   10.292%   $25.8635   $25.86   $25.85   $25.90  
  Purchase #5 $178.82   13.181%   $202.3903   $202.39   $202.40   $202.40  
  Purchase #6 $216.84   11.114%   $240.9396   $240.94   $240.95   $240.90  
  Purchase #7 $108.99   13.654%   $123.8715   $123.87   $123.85   $123.90  
  7 purchase totals = $897.20       $994.0914   $994.09   $994.10   $994.10