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 $42.82   13.460%   $48.5836   $48.58   $48.60   $48.60  
  Purchase #2 $204.44   6.199%   $217.1132   $217.11   $217.10   $217.10  
  Purchase #3 $105.67   10.561%   $116.8298   $116.83   $116.85   $116.80  
  Purchase #4 $167.54   9.607%   $183.6356   $183.64   $183.65   $183.60  
  Purchase #5 $116.54   9.159%   $127.2139   $127.21   $127.20   $127.20  
  Purchase #6 $102.51   12.329%   $115.1485   $115.15   $115.15   $115.10  
  Purchase #7 $70.29   4.105%   $73.1754   $73.18   $73.20   $73.20  
  7 purchase totals = $809.81       $881.7000   $881.70   $881.75   $881.60