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 $123.58   8.128%   $133.6246   $133.62   $133.60   $133.60  
  Purchase #2 $215.53   13.759%   $245.1848   $245.18   $245.20   $245.20  
  Purchase #3 $183.96   9.333%   $201.129   $201.13   $201.15   $201.10  
  Purchase #4 $74.46   4.233%   $77.6119   $77.61   $77.60   $77.60  
  Purchase #5 $97.69   11.581%   $109.0035   $109.00   $109.00   $109.00  
  Purchase #6 $241.71   4.205%   $251.8739   $251.87   $251.85   $251.90  
  Purchase #7 $126.38   5.153%   $132.8924   $132.89   $132.90   $132.90  
  7 purchase totals = $1,063.31       $1,151.3201   $1,151.30   $1,151.30   $1,151.30