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 $246.80   7.482%   $265.2656   $265.27   $265.25   $265.30  
  Purchase #2 $118.93   5.676%   $125.6805   $125.68   $125.70   $125.70  
  Purchase #3 $79.52   8.608%   $86.3651   $86.37   $86.35   $86.40  
  Purchase #4 $193.39   4.120%   $201.3577   $201.36   $201.35   $201.40  
  Purchase #5 $54.74   8.475%   $59.3792   $59.38   $59.40   $59.40  
  Purchase #6 $43.76   6.709%   $46.6959   $46.70   $46.70   $46.70  
  Purchase #7 $201.50   3.113%   $207.7727   $207.77   $207.75   $207.80  
  7 purchase totals = $938.64       $992.5167   $992.53   $992.50   $992.70