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 $96.38   10.757%   $106.7476   $106.75   $106.75   $106.70  
  Purchase #2 $205.35   6.621%   $218.9462   $218.95   $218.95   $218.90  
  Purchase #3 $46.90   10.177%   $51.673   $51.67   $51.65   $51.70  
  Purchase #4 $49.54   7.448%   $53.2297   $53.23   $53.25   $53.20  
  Purchase #5 $44.62   6.751%   $47.6323   $47.63   $47.65   $47.60  
  Purchase #6 $89.57   12.712%   $100.9561   $100.96   $100.95   $101.00  
  Purchase #7 $30.32   9.409%   $33.1728   $33.17   $33.15   $33.20  
  7 purchase totals = $562.68       $612.3577   $612.36   $612.35   $612.30