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 $163.67   12.428%   $184.0109   $184.01   $184.00   $184.00  
  Purchase #2 $86.95   8.853%   $94.6477   $94.65   $94.65   $94.60  
  Purchase #3 $212.42   11.176%   $236.1601   $236.16   $236.15   $236.20  
  Purchase #4 $179.77   11.519%   $200.4777   $200.48   $200.50   $200.50  
  Purchase #5 $45.50   7.103%   $48.7319   $48.73   $48.75   $48.70  
  Purchase #6 $114.74   4.507%   $119.9113   $119.91   $119.90   $119.90  
  Purchase #7 $181.25   3.469%   $187.5376   $187.54   $187.55   $187.50  
  7 purchase totals = $984.30       $1,071.4772   $1,071.48   $1,071.50   $1,071.40