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 $212.99   10.210%   $234.7363   $234.74   $234.75   $234.70  
  Purchase #2 $84.38   8.688%   $91.7109   $91.71   $91.70   $91.70  
  Purchase #3 $46.31   3.113%   $47.7516   $47.75   $47.75   $47.80  
  Purchase #4 $95.77   8.342%   $103.7591   $103.76   $103.75   $103.80  
  Purchase #5 $32.86   6.691%   $35.0587   $35.06   $35.05   $35.10  
  Purchase #6 $113.45   4.184%   $118.1967   $118.20   $118.20   $118.20  
  Purchase #7 $125.72   6.691%   $134.1319   $134.13   $134.15   $134.10  
  7 purchase totals = $711.48       $765.3452   $765.35   $765.35   $765.40