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 $69.72   13.727%   $79.2905   $79.29   $79.30   $79.30  
  Purchase #2 $167.37   9.228%   $182.8149   $182.81   $182.80   $182.80  
  Purchase #3 $126.39   4.745%   $132.3872   $132.39   $132.40   $132.40  
  Purchase #4 $215.26   3.628%   $223.0696   $223.07   $223.05   $223.10  
  Purchase #5 $30.75   13.201%   $34.8093   $34.81   $34.80   $34.80  
  Purchase #6 $99.76   6.559%   $106.3033   $106.30   $106.30   $106.30  
  Purchase #7 $224.61   13.512%   $254.9593   $254.96   $254.95   $255.00  
  7 purchase totals = $933.86       $1,013.6341   $1,013.63   $1,013.60   $1,013.70