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 $92.66   3.826%   $96.2052   $96.21   $96.20   $96.20  
  Purchase #2 $211.33   13.198%   $239.2213   $239.22   $239.20   $239.20  
  Purchase #3 $101.36   9.271%   $110.7571   $110.76   $110.75   $110.80  
  Purchase #4 $129.35   8.278%   $140.0576   $140.06   $140.05   $140.10  
  Purchase #5 $242.67   8.867%   $264.1875   $264.19   $264.20   $264.20  
  Purchase #6 $42.33   12.519%   $47.6293   $47.63   $47.65   $47.60  
  Purchase #7 $212.52   13.599%   $241.4206   $241.42   $241.40   $241.40  
  7 purchase totals = $1,032.22       $1,139.4786   $1,139.49   $1,139.45   $1,139.50