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 $204.59   4.259%   $213.3035   $213.30   $213.30   $213.30  
  Purchase #2 $229.61   9.630%   $251.7214   $251.72   $251.70   $251.70  
  Purchase #3 $18.91   9.275%   $20.6639   $20.66   $20.65   $20.70  
  Purchase #4 $101.58   5.367%   $107.0318   $107.03   $107.05   $107.00  
  Purchase #5 $92.62   7.172%   $99.2627   $99.26   $99.25   $99.30  
  Purchase #6 $226.47   8.452%   $245.6112   $245.61   $245.60   $245.60  
  Purchase #7 $29.26   3.319%   $30.2311   $30.23   $30.25   $30.20  
  7 purchase totals = $903.04       $967.8256   $967.81   $967.80   $967.80