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 $49.40   10.661%   $54.6665   $54.67   $54.65   $54.70  
  Purchase #2 $249.52   4.673%   $261.1801   $261.18   $261.20   $261.20  
  Purchase #3 $221.61   4.635%   $231.8816   $231.88   $231.90   $231.90  
  Purchase #4 $167.37   4.285%   $174.5418   $174.54   $174.55   $174.50  
  Purchase #5 $117.71   7.502%   $126.5406   $126.54   $126.55   $126.50  
  Purchase #6 $236.98   3.265%   $244.7174   $244.72   $244.70   $244.70  
  Purchase #7 $228.55   9.727%   $250.7811   $250.78   $250.80   $250.80  
  7 purchase totals = $1,271.14       $1,344.3091   $1,344.31   $1,344.35   $1,344.30