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 $47.71   11.711%   $53.2973   $53.30   $53.30   $53.30  
  Purchase #2 $233.95   4.219%   $243.8204   $243.82   $243.80   $243.80  
  Purchase #3 $45.78   7.179%   $49.0665   $49.07   $49.05   $49.10  
  Purchase #4 $200.91   4.353%   $209.6556   $209.66   $209.65   $209.70  
  Purchase #5 $15.30   6.496%   $16.2939   $16.29   $16.30   $16.30  
  Purchase #6 $190.54   6.459%   $202.847   $202.85   $202.85   $202.80  
  Purchase #7 $117.87   6.228%   $125.2109   $125.21   $125.20   $125.20  
  7 purchase totals = $852.06       $900.1916   $900.20   $900.15   $900.20