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 $58.28   13.173%   $65.9572   $65.96   $65.95   $66.00  
  Purchase #2 $247.59   7.177%   $265.3595   $265.36   $265.35   $265.40  
  Purchase #3 $148.49   9.182%   $162.1244   $162.12   $162.10   $162.10  
  Purchase #4 $245.95   13.691%   $279.623   $279.62   $279.60   $279.60  
  Purchase #5 $217.47   6.583%   $231.7861   $231.79   $231.80   $231.80  
  Purchase #6 $158.74   11.173%   $176.476   $176.48   $176.50   $176.50  
  Purchase #7 $76.95   3.244%   $79.4463   $79.45   $79.45   $79.40  
  7 purchase totals = $1,153.47       $1,260.7725   $1,260.78   $1,260.75   $1,260.80