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 $23.86   7.362%   $25.6166   $25.62   $25.60   $25.60  
  Purchase #2 $234.96   4.599%   $245.7658   $245.77   $245.75   $245.80  
  Purchase #3 $199.27   13.597%   $226.3647   $226.36   $226.35   $226.40  
  Purchase #4 $107.61   7.840%   $116.0466   $116.05   $116.05   $116.00  
  Purchase #5 $51.63   8.593%   $56.0666   $56.07   $56.05   $56.10  
  Purchase #6 $72.50   3.102%   $74.749   $74.75   $74.75   $74.70  
  Purchase #7 $24.54   7.149%   $26.2944   $26.29   $26.30   $26.30  
  7 purchase totals = $714.37       $770.9037   $770.91   $770.85   $770.90