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 $63.40   8.283%   $68.6514   $68.65   $68.65   $68.70  
  Purchase #2 $64.27   13.496%   $72.9439   $72.94   $72.95   $72.90  
  Purchase #3 $189.45   12.105%   $212.3829   $212.38   $212.40   $212.40  
  Purchase #4 $202.27   6.233%   $214.8775   $214.88   $214.90   $214.90  
  Purchase #5 $114.48   7.403%   $122.955   $122.96   $122.95   $123.00  
  Purchase #6 $102.88   11.620%   $114.8347   $114.83   $114.85   $114.80  
  Purchase #7 $196.74   9.610%   $215.6467   $215.65   $215.65   $215.60  
  7 purchase totals = $933.49       $1,022.2921   $1,022.29   $1,022.35   $1,022.30