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 $67.68   8.193%   $73.225   $73.23   $73.25   $73.20  
  Purchase #2 $125.49   7.241%   $134.5767   $134.58   $134.60   $134.60  
  Purchase #3 $27.38   8.697%   $29.7612   $29.76   $29.75   $29.80  
  Purchase #4 $7.43   13.715%   $8.449   $8.45   $8.45   $8.40  
  Purchase #5 $202.63   5.207%   $213.1809   $213.18   $213.20   $213.20  
  Purchase #6 $201.98   10.869%   $223.9332   $223.93   $223.95   $223.90  
  Purchase #7 $60.45   6.225%   $64.213   $64.21   $64.20   $64.20  
  7 purchase totals = $693.04       $747.3390   $747.34   $747.40   $747.30