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 $125.67   6.595%   $133.9579   $133.96   $133.95   $134.00  
  Purchase #2 $90.68   6.857%   $96.8979   $96.90   $96.90   $96.90  
  Purchase #3 $187.60   6.243%   $199.3119   $199.31   $199.30   $199.30  
  Purchase #4 $195.72   4.854%   $205.2202   $205.22   $205.20   $205.20  
  Purchase #5 $70.90   6.702%   $75.6517   $75.65   $75.65   $75.70  
  Purchase #6 $222.51   8.771%   $242.0264   $242.03   $242.05   $242.00  
  Purchase #7 $123.92   7.647%   $133.3962   $133.40   $133.40   $133.40  
  7 purchase totals = $1,017.00       $1,086.4622   $1,086.47   $1,086.45   $1,086.50