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 $61.27   6.117%   $65.0179   $65.02   $65.00   $65.00  
  Purchase #2 $119.31   11.324%   $132.8207   $132.82   $132.80   $132.80  
  Purchase #3 $73.65   12.817%   $83.0897   $83.09   $83.10   $83.10  
  Purchase #4 $52.94   7.287%   $56.7977   $56.80   $56.80   $56.80  
  Purchase #5 $143.50   12.714%   $161.7446   $161.74   $161.75   $161.70  
  Purchase #6 $221.80   8.325%   $240.2649   $240.26   $240.25   $240.30  
  Purchase #7 $156.55   8.832%   $170.3765   $170.38   $170.40   $170.40  
  7 purchase totals = $829.02       $910.1120   $910.11   $910.10   $910.10