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 $32.27   12.361%   $36.2589   $36.26   $36.25   $36.30  
  Purchase #2 $196.54   10.506%   $217.1885   $217.19   $217.20   $217.20  
  Purchase #3 $243.96   11.746%   $272.6155   $272.62   $272.60   $272.60  
  Purchase #4 $82.73   6.378%   $88.0065   $88.01   $88.00   $88.00  
  Purchase #5 $117.68   7.151%   $126.0953   $126.10   $126.10   $126.10  
  Purchase #6 $40.76   9.715%   $44.7198   $44.72   $44.70   $44.70  
  Purchase #7 $155.45   10.526%   $171.8127   $171.81   $171.80   $171.80  
  7 purchase totals = $869.39       $956.6972   $956.71   $956.65   $956.70