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 $110.97   6.752%   $118.4627   $118.46   $118.45   $118.50  
  Purchase #2 $181.41   6.417%   $193.0511   $193.05   $193.05   $193.10  
  Purchase #3 $242.85   11.616%   $271.0595   $271.06   $271.05   $271.10  
  Purchase #4 $233.39   5.153%   $245.4166   $245.42   $245.40   $245.40  
  Purchase #5 $87.55   8.327%   $94.8403   $94.84   $94.85   $94.80  
  Purchase #6 $157.75   5.823%   $166.9358   $166.94   $166.95   $166.90  
  Purchase #7 $182.91   4.579%   $191.2854   $191.29   $191.30   $191.30  
  7 purchase totals = $1,196.83       $1,281.0514   $1,281.06   $1,281.05   $1,281.10