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 $207.59   12.662%   $233.875   $233.88   $233.90   $233.90  
  Purchase #2 $205.32   8.633%   $223.0453   $223.05   $223.05   $223.00  
  Purchase #3 $98.31   13.675%   $111.7539   $111.75   $111.75   $111.80  
  Purchase #4 $199.34   4.697%   $208.703   $208.70   $208.70   $208.70  
  Purchase #5 $41.39   12.595%   $46.6031   $46.60   $46.60   $46.60  
  Purchase #6 $212.37   8.185%   $229.7525   $229.75   $229.75   $229.80  
  Purchase #7 $156.47   6.758%   $167.0442   $167.04   $167.05   $167.00  
  7 purchase totals = $1,120.79       $1,220.7770   $1,220.77   $1,220.80   $1,220.80