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 $150.67   7.608%   $162.133   $162.13   $162.15   $162.10  
  Purchase #2 $25.82   5.211%   $27.1655   $27.17   $27.15   $27.20  
  Purchase #3 $131.72   4.226%   $137.2865   $137.29   $137.30   $137.30  
  Purchase #4 $181.28   6.784%   $193.578   $193.58   $193.60   $193.60  
  Purchase #5 $220.85   5.772%   $233.5975   $233.60   $233.60   $233.60  
  Purchase #6 $220.77   6.843%   $235.8773   $235.88   $235.90   $235.90  
  Purchase #7 $248.63   10.447%   $274.6044   $274.60   $274.60   $274.60  
  7 purchase totals = $1,179.74       $1,264.2422   $1,264.25   $1,264.30   $1,264.30