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 $110.57   13.661%   $125.675   $125.68   $125.70   $125.70  
  Purchase #2 $50.73   12.799%   $57.2229   $57.22   $57.20   $57.20  
  Purchase #3 $68.93   4.135%   $71.7803   $71.78   $71.80   $71.80  
  Purchase #4 $229.96   13.628%   $261.2989   $261.30   $261.30   $261.30  
  Purchase #5 $165.71   7.582%   $178.2741   $178.27   $178.25   $178.30  
  Purchase #6 $126.34   13.713%   $143.665   $143.67   $143.65   $143.70  
  Purchase #7 $120.61   8.171%   $130.465   $130.47   $130.45   $130.50  
  7 purchase totals = $872.85       $968.3812   $968.39   $968.35   $968.50