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 $202.62   5.123%   $213.0002   $213.00   $213.00   $213.00  
  Purchase #2 $75.85   6.732%   $80.9562   $80.96   $80.95   $81.00  
  Purchase #3 $82.85   3.359%   $85.6329   $85.63   $85.65   $85.60  
  Purchase #4 $104.81   7.854%   $113.0418   $113.04   $113.05   $113.00  
  Purchase #5 $64.93   11.741%   $72.5534   $72.55   $72.55   $72.60  
  Purchase #6 $64.59   13.355%   $73.216   $73.22   $73.20   $73.20  
  Purchase #7 $96.34   13.756%   $109.5925   $109.59   $109.60   $109.60  
  7 purchase totals = $691.99       $747.9930   $747.99   $748.00   $748.00