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 $34.57   8.199%   $37.4044   $37.40   $37.40   $37.40  
  Purchase #2 $163.56   10.585%   $180.8728   $180.87   $180.85   $180.90  
  Purchase #3 $68.56   12.662%   $77.2411   $77.24   $77.25   $77.20  
  Purchase #4 $16.32   7.407%   $17.5288   $17.53   $17.55   $17.50  
  Purchase #5 $242.55   11.711%   $270.955   $270.96   $270.95   $271.00  
  Purchase #6 $104.92   6.413%   $111.6485   $111.65   $111.65   $111.60  
  Purchase #7 $63.90   3.785%   $66.3186   $66.32   $66.30   $66.30  
  7 purchase totals = $694.38       $761.9692   $761.97   $761.95   $761.90