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 $171.62   6.807%   $183.3022   $183.30   $183.30   $183.30  
  Purchase #2 $54.27   3.556%   $56.1998   $56.20   $56.20   $56.20  
  Purchase #3 $188.39   4.460%   $196.7922   $196.79   $196.80   $196.80  
  Purchase #4 $244.62   4.614%   $255.9068   $255.91   $255.90   $255.90  
  Purchase #5 $239.99   10.707%   $265.6857   $265.69   $265.70   $265.70  
  Purchase #6 $195.92   4.764%   $205.2536   $205.25   $205.25   $205.30  
  Purchase #7 $28.40   6.642%   $30.2863   $30.29   $30.30   $30.30  
  7 purchase totals = $1,123.21       $1,193.4266   $1,193.43   $1,193.45   $1,193.50