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 $66.87   12.348%   $75.1271   $75.13   $75.15   $75.10  
  Purchase #2 $113.78   5.481%   $120.0163   $120.02   $120.00   $120.00  
  Purchase #3 $139.96   4.666%   $146.4905   $146.49   $146.50   $146.50  
  Purchase #4 $120.99   4.456%   $126.3813   $126.38   $126.40   $126.40  
  Purchase #5 $197.71   11.400%   $220.2489   $220.25   $220.25   $220.20  
  Purchase #6 $48.27   9.812%   $53.0063   $53.01   $53.00   $53.00  
  Purchase #7 $13.86   3.780%   $14.3839   $14.38   $14.40   $14.40  
  7 purchase totals = $701.44       $755.6543   $755.66   $755.70   $755.60