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 $58.46   9.279%   $63.8845   $63.88   $63.90   $63.90  
  Purchase #2 $131.83   7.819%   $142.1378   $142.14   $142.15   $142.10  
  Purchase #3 $129.58   12.152%   $145.3266   $145.33   $145.35   $145.30  
  Purchase #4 $74.45   3.475%   $77.0371   $77.04   $77.05   $77.00  
  Purchase #5 $116.49   9.134%   $127.1302   $127.13   $127.15   $127.10  
  Purchase #6 $125.29   10.447%   $138.379   $138.38   $138.40   $138.40  
  Purchase #7 $97.43   4.223%   $101.5445   $101.54   $101.55   $101.50  
  7 purchase totals = $733.53       $795.4397   $795.44   $795.55   $795.30