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 $209.48   11.359%   $233.2748   $233.27   $233.25   $233.30  
  Purchase #2 $87.81   7.713%   $94.5828   $94.58   $94.60   $94.60  
  Purchase #3 $123.66   7.673%   $133.1484   $133.15   $133.15   $133.10  
  Purchase #4 $166.80   8.441%   $180.8796   $180.88   $180.90   $180.90  
  Purchase #5 $234.99   3.725%   $243.7434   $243.74   $243.75   $243.70  
  Purchase #6 $91.39   13.717%   $103.926   $103.93   $103.95   $103.90  
  Purchase #7 $199.87   7.216%   $214.2926   $214.29   $214.30   $214.30  
  7 purchase totals = $1,114.00       $1,203.8476   $1,203.84   $1,203.90   $1,203.80