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 $54.38   5.689%   $57.4737   $57.47   $57.45   $57.50  
  Purchase #2 $152.63   5.490%   $161.0094   $161.01   $161.00   $161.00  
  Purchase #3 $142.98   4.211%   $149.0009   $149.00   $149.00   $149.00  
  Purchase #4 $71.37   5.565%   $75.3417   $75.34   $75.35   $75.30  
  Purchase #5 $207.35   8.350%   $224.6637   $224.66   $224.65   $224.70  
  Purchase #6 $227.25   7.589%   $244.496   $244.50   $244.50   $244.50  
  Purchase #7 $87.81   10.847%   $97.3348   $97.33   $97.35   $97.30  
  7 purchase totals = $943.77       $1,009.3202   $1,009.31   $1,009.30   $1,009.30