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 $230.38   11.383%   $256.6042   $256.60   $256.60   $256.60  
  Purchase #2 $195.87   4.282%   $204.2572   $204.26   $204.25   $204.30  
  Purchase #3 $211.96   10.336%   $233.8682   $233.87   $233.85   $233.90  
  Purchase #4 $161.33   7.453%   $173.3539   $173.35   $173.35   $173.40  
  Purchase #5 $101.61   3.516%   $105.1826   $105.18   $105.20   $105.20  
  Purchase #6 $165.26   5.869%   $174.9591   $174.96   $174.95   $175.00  
  Purchase #7 $184.31   13.582%   $209.343   $209.34   $209.35   $209.30  
  7 purchase totals = $1,250.72       $1,357.5682   $1,357.56   $1,357.55   $1,357.70