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 $114.93   3.393%   $118.8296   $118.83   $118.85   $118.80  
  Purchase #2 $172.83   6.476%   $184.0225   $184.02   $184.00   $184.00  
  Purchase #3 $169.70   6.515%   $180.756   $180.76   $180.75   $180.80  
  Purchase #4 $98.36   3.468%   $101.7711   $101.77   $101.75   $101.80  
  Purchase #5 $52.99   6.225%   $56.2886   $56.29   $56.30   $56.30  
  Purchase #6 $208.66   5.452%   $220.0361   $220.04   $220.05   $220.00  
  Purchase #7 $203.51   10.170%   $224.207   $224.21   $224.20   $224.20  
  7 purchase totals = $1,020.98       $1,085.9109   $1,085.92   $1,085.90   $1,085.90