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 $228.43   11.117%   $253.8246   $253.82   $253.80   $253.80  
  Purchase #2 $61.73   10.674%   $68.3191   $68.32   $68.30   $68.30  
  Purchase #3 $142.42   5.787%   $150.6618   $150.66   $150.65   $150.70  
  Purchase #4 $155.72   8.416%   $168.8254   $168.83   $168.85   $168.80  
  Purchase #5 $159.73   11.466%   $178.0446   $178.04   $178.05   $178.00  
  Purchase #6 $46.41   3.575%   $48.0692   $48.07   $48.05   $48.10  
  Purchase #7 $76.66   8.302%   $83.0243   $83.02   $83.00   $83.00  
  7 purchase totals = $871.10       $950.7690   $950.76   $950.70   $950.70