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 $60.51   12.686%   $68.1863   $68.19   $68.20   $68.20  
  Purchase #2 $187.73   10.282%   $207.0324   $207.03   $207.05   $207.00  
  Purchase #3 $40.50   5.504%   $42.7291   $42.73   $42.75   $42.70  
  Purchase #4 $180.97   3.425%   $187.1682   $187.17   $187.15   $187.20  
  Purchase #5 $76.61   12.593%   $86.2575   $86.26   $86.25   $86.30  
  Purchase #6 $224.58   13.457%   $254.8017   $254.80   $254.80   $254.80  
  Purchase #7 $181.33   10.311%   $200.0269   $200.03   $200.05   $200.00  
  7 purchase totals = $952.23       $1,046.2021   $1,046.21   $1,046.25   $1,046.20