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 $223.40   8.308%   $241.9601   $241.96   $241.95   $242.00  
  Purchase #2 $242.58   7.127%   $259.8687   $259.87   $259.85   $259.90  
  Purchase #3 $203.26   8.130%   $219.785   $219.79   $219.80   $219.80  
  Purchase #4 $244.96   4.647%   $256.3433   $256.34   $256.35   $256.30  
  Purchase #5 $104.97   11.616%   $117.1633   $117.16   $117.15   $117.20  
  Purchase #6 $231.96   3.474%   $240.0183   $240.02   $240.00   $240.00  
  Purchase #7 $94.61   3.780%   $98.1863   $98.19   $98.20   $98.20  
  7 purchase totals = $1,345.74       $1,433.3250   $1,433.33   $1,433.30   $1,433.40