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 $241.44   11.223%   $268.5368   $268.54   $268.55   $268.50  
  Purchase #2 $177.68   9.682%   $194.883   $194.88   $194.90   $194.90  
  Purchase #3 $73.99   6.185%   $78.5663   $78.57   $78.55   $78.60  
  Purchase #4 $125.30   4.786%   $131.2969   $131.30   $131.30   $131.30  
  Purchase #5 $186.31   9.756%   $204.4864   $204.49   $204.50   $204.50  
  Purchase #6 $165.72   13.208%   $187.6083   $187.61   $187.60   $187.60  
  Purchase #7 $97.80   8.561%   $106.1727   $106.17   $106.15   $106.20  
  7 purchase totals = $1,068.24       $1,171.5504   $1,171.56   $1,171.55   $1,171.60