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 $60.59   5.663%   $64.0212   $64.02   $64.00   $64.00  
  Purchase #2 $138.79   3.847%   $144.1293   $144.13   $144.15   $144.10  
  Purchase #3 $250.61   6.565%   $267.0625   $267.06   $267.05   $267.10  
  Purchase #4 $175.78   5.434%   $185.3319   $185.33   $185.35   $185.30  
  Purchase #5 $93.45   11.734%   $104.4154   $104.42   $104.40   $104.40  
  Purchase #6 $13.97   13.547%   $15.8625   $15.86   $15.85   $15.90  
  Purchase #7 $210.92   13.635%   $239.6789   $239.68   $239.70   $239.70  
  7 purchase totals = $944.11       $1,020.5017   $1,020.50   $1,020.50   $1,020.50