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 $57.36   11.499%   $63.9558   $63.96   $63.95   $64.00  
  Purchase #2 $139.62   13.624%   $158.6418   $158.64   $158.65   $158.60  
  Purchase #3 $183.68   11.501%   $204.805   $204.81   $204.80   $204.80  
  Purchase #4 $133.90   5.673%   $141.4961   $141.50   $141.50   $141.50  
  Purchase #5 $93.25   12.322%   $104.7403   $104.74   $104.75   $104.70  
  Purchase #6 $115.25   12.215%   $129.3278   $129.33   $129.35   $129.30  
  Purchase #7 $109.96   5.561%   $116.0749   $116.07   $116.05   $116.10  
  7 purchase totals = $833.02       $919.0417   $919.05   $919.05   $919.00