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 $40.84   10.671%   $45.198   $45.20   $45.20   $45.20  
  Purchase #2 $50.58   4.659%   $52.9365   $52.94   $52.95   $52.90  
  Purchase #3 $62.85   11.481%   $70.0658   $70.07   $70.05   $70.10  
  Purchase #4 $70.62   3.669%   $73.211   $73.21   $73.20   $73.20  
  Purchase #5 $85.50   12.469%   $96.161   $96.16   $96.15   $96.20  
  Purchase #6 $47.90   11.831%   $53.567   $53.57   $53.55   $53.60  
  Purchase #7 $166.47   8.587%   $180.7648   $180.76   $180.75   $180.80  
  7 purchase totals = $524.76       $571.9041   $571.91   $571.85   $572.00