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 $61.74   5.481%   $65.124   $65.12   $65.10   $65.10  
  Purchase #2 $66.73   10.637%   $73.8281   $73.83   $73.85   $73.80  
  Purchase #3 $217.56   7.525%   $233.9314   $233.93   $233.95   $233.90  
  Purchase #4 $23.48   5.698%   $24.8179   $24.82   $24.80   $24.80  
  Purchase #5 $153.75   9.655%   $168.5946   $168.59   $168.60   $168.60  
  Purchase #6 $119.39   11.766%   $133.4374   $133.44   $133.45   $133.40  
  Purchase #7 $43.62   9.579%   $47.7984   $47.80   $47.80   $47.80  
  7 purchase totals = $686.27       $747.5318   $747.53   $747.55   $747.40