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 $51.39   5.747%   $54.3434   $54.34   $54.35   $54.30  
  Purchase #2 $180.70   11.359%   $201.2257   $201.23   $201.25   $201.20  
  Purchase #3 $67.30   13.425%   $76.335   $76.34   $76.35   $76.30  
  Purchase #4 $130.33   4.127%   $135.7087   $135.71   $135.70   $135.70  
  Purchase #5 $173.36   3.793%   $179.9355   $179.94   $179.95   $179.90  
  Purchase #6 $174.50   9.567%   $191.1944   $191.19   $191.20   $191.20  
  Purchase #7 $84.61   9.357%   $92.527   $92.53   $92.55   $92.50  
  7 purchase totals = $862.19       $931.2697   $931.28   $931.35   $931.10