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 $223.49   11.852%   $249.978   $249.98   $250.00   $250.00  
  Purchase #2 $141.81   3.779%   $147.169   $147.17   $147.15   $147.20  
  Purchase #3 $194.68   4.381%   $203.2089   $203.21   $203.20   $203.20  
  Purchase #4 $158.47   11.629%   $176.8985   $176.90   $176.90   $176.90  
  Purchase #5 $218.88   8.749%   $238.0298   $238.03   $238.05   $238.00  
  Purchase #6 $127.38   12.612%   $143.4452   $143.45   $143.45   $143.40  
  Purchase #7 $167.82   11.673%   $187.4096   $187.41   $187.40   $187.40  
  7 purchase totals = $1,232.53       $1,346.1390   $1,346.15   $1,346.15   $1,346.10