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 $18.32   10.181%   $20.1852   $20.19   $20.20   $20.20  
  Purchase #2 $212.74   3.644%   $220.4922   $220.49   $220.50   $220.50  
  Purchase #3 $215.66   4.685%   $225.7637   $225.76   $225.75   $225.80  
  Purchase #4 $189.94   13.209%   $215.0292   $215.03   $215.05   $215.00  
  Purchase #5 $41.45   13.716%   $47.1353   $47.14   $47.15   $47.10  
  Purchase #6 $75.53   9.375%   $82.6109   $82.61   $82.60   $82.60  
  Purchase #7 $133.90   12.503%   $150.6415   $150.64   $150.65   $150.60  
  7 purchase totals = $887.54       $961.8580   $961.86   $961.90   $961.80