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 $166.98   11.798%   $186.6803   $186.68   $186.70   $186.70  
  Purchase #2 $97.38   4.450%   $101.7134   $101.71   $101.70   $101.70  
  Purchase #3 $26.65   3.697%   $27.6353   $27.64   $27.65   $27.60  
  Purchase #4 $39.86   11.124%   $44.294   $44.29   $44.30   $44.30  
  Purchase #5 $19.76   4.591%   $20.6672   $20.67   $20.65   $20.70  
  Purchase #6 $200.44   4.588%   $209.6362   $209.64   $209.65   $209.60  
  Purchase #7 $163.40   5.787%   $172.856   $172.86   $172.85   $172.90  
  7 purchase totals = $714.47       $763.4824   $763.49   $763.50   $763.50