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 $183.38   12.295%   $205.9266   $205.93   $205.95   $205.90  
  Purchase #2 $210.83   10.625%   $233.2307   $233.23   $233.25   $233.20  
  Purchase #3 $96.64   4.505%   $100.9936   $100.99   $101.00   $101.00  
  Purchase #4 $197.43   7.665%   $212.563   $212.56   $212.55   $212.60  
  Purchase #5 $225.70   8.491%   $244.8642   $244.86   $244.85   $244.90  
  Purchase #6 $201.46   10.832%   $223.2821   $223.28   $223.30   $223.30  
  Purchase #7 $58.60   4.379%   $61.1661   $61.17   $61.15   $61.20  
  7 purchase totals = $1,174.04       $1,282.0263   $1,282.02   $1,282.05   $1,282.10