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 $248.93   13.228%   $281.8585   $281.86   $281.85   $281.90  
  Purchase #2 $248.62   9.163%   $271.4011   $271.40   $271.40   $271.40  
  Purchase #3 $157.33   3.345%   $162.5927   $162.59   $162.60   $162.60  
  Purchase #4 $107.72   4.689%   $112.771   $112.77   $112.75   $112.80  
  Purchase #5 $105.82   4.226%   $110.292   $110.29   $110.30   $110.30  
  Purchase #6 $135.93   4.182%   $141.6146   $141.61   $141.60   $141.60  
  Purchase #7 $231.73   9.529%   $253.8116   $253.81   $253.80   $253.80  
  7 purchase totals = $1,236.08       $1,334.3415   $1,334.33   $1,334.30   $1,334.40