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 $89.66   3.199%   $92.5282   $92.53   $92.55   $92.50  
  Purchase #2 $172.95   11.636%   $193.0745   $193.07   $193.05   $193.10  
  Purchase #3 $37.61   6.834%   $40.1803   $40.18   $40.20   $40.20  
  Purchase #4 $46.43   11.315%   $51.6836   $51.68   $51.70   $51.70  
  Purchase #5 $62.39   6.384%   $66.373   $66.37   $66.35   $66.40  
  Purchase #6 $176.41   10.328%   $194.6296   $194.63   $194.65   $194.60  
  Purchase #7 $95.52   7.389%   $102.578   $102.58   $102.60   $102.60  
  7 purchase totals = $680.97       $741.0472   $741.04   $741.10   $741.10