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 $249.65   5.739%   $263.9774   $263.98   $264.00   $264.00  
  Purchase #2 $158.69   13.121%   $179.5117   $179.51   $179.50   $179.50  
  Purchase #3 $156.69   3.492%   $162.1616   $162.16   $162.15   $162.20  
  Purchase #4 $185.92   7.556%   $199.9681   $199.97   $199.95   $200.00  
  Purchase #5 $104.46   9.698%   $114.5905   $114.59   $114.60   $114.60  
  Purchase #6 $165.80   5.439%   $174.8179   $174.82   $174.80   $174.80  
  Purchase #7 $21.78   10.248%   $24.012   $24.01   $24.00   $24.00  
  7 purchase totals = $1,042.99       $1,119.0392   $1,119.04   $1,119.00   $1,119.10