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 $104.35   11.299%   $116.1405   $116.14   $116.15   $116.10  
  Purchase #2 $96.72   11.275%   $107.6252   $107.63   $107.65   $107.60  
  Purchase #3 $231.91   11.282%   $258.0741   $258.07   $258.05   $258.10  
  Purchase #4 $92.68   10.296%   $102.2223   $102.22   $102.20   $102.20  
  Purchase #5 $33.90   5.658%   $35.8181   $35.82   $35.80   $35.80  
  Purchase #6 $17.51   10.163%   $19.2895   $19.29   $19.30   $19.30  
  Purchase #7 $199.88   7.322%   $214.5152   $214.52   $214.50   $214.50  
  7 purchase totals = $776.95       $853.6849   $853.69   $853.65   $853.60