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 $118.67   6.389%   $126.2518   $126.25   $126.25   $126.30  
  Purchase #2 $127.99   10.727%   $141.7195   $141.72   $141.70   $141.70  
  Purchase #3 $227.38   7.455%   $244.3312   $244.33   $244.35   $244.30  
  Purchase #4 $15.34   10.452%   $16.9433   $16.94   $16.95   $16.90  
  Purchase #5 $221.67   4.450%   $231.5343   $231.53   $231.55   $231.50  
  Purchase #6 $162.85   9.715%   $178.6709   $178.67   $178.65   $178.70  
  Purchase #7 $210.48   7.779%   $226.8532   $226.85   $226.85   $226.90  
  7 purchase totals = $1,084.38       $1,166.3042   $1,166.29   $1,166.30   $1,166.30