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 $104.33   11.296%   $116.1151   $116.12   $116.10   $116.10  
  Purchase #2 $175.71   6.578%   $187.2682   $187.27   $187.25   $187.30  
  Purchase #3 $162.36   10.664%   $179.6741   $179.67   $179.65   $179.70  
  Purchase #4 $248.46   6.403%   $264.3689   $264.37   $264.35   $264.40  
  Purchase #5 $46.62   4.852%   $48.882   $48.88   $48.90   $48.90  
  Purchase #6 $25.77   12.789%   $29.0657   $29.07   $29.05   $29.10  
  Purchase #7 $122.63   5.237%   $129.0521   $129.05   $129.05   $129.10  
  7 purchase totals = $885.88       $954.4261   $954.43   $954.35   $954.60