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 $183.86   11.601%   $205.1896   $205.19   $205.20   $205.20  
  Purchase #2 $102.98   12.763%   $116.1233   $116.12   $116.10   $116.10  
  Purchase #3 $101.27   12.477%   $113.9055   $113.91   $113.90   $113.90  
  Purchase #4 $129.94   4.838%   $136.2265   $136.23   $136.25   $136.20  
  Purchase #5 $178.56   12.544%   $200.9586   $200.96   $200.95   $201.00  
  Purchase #6 $239.72   12.573%   $269.86   $269.86   $269.85   $269.90  
  Purchase #7 $240.46   4.221%   $250.6098   $250.61   $250.60   $250.60  
  7 purchase totals = $1,176.79       $1,292.8733   $1,292.88   $1,292.85   $1,292.90