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 $244.65   9.667%   $268.3003   $268.30   $268.30   $268.30  
  Purchase #2 $158.96   9.703%   $174.3839   $174.38   $174.40   $174.40  
  Purchase #3 $58.56   5.240%   $61.6285   $61.63   $61.65   $61.60  
  Purchase #4 $238.46   3.146%   $245.962   $245.96   $245.95   $246.00  
  Purchase #5 $211.37   8.204%   $228.7108   $228.71   $228.70   $228.70  
  Purchase #6 $164.85   13.792%   $187.5861   $187.59   $187.60   $187.60  
  Purchase #7 $114.43   10.683%   $126.6546   $126.65   $126.65   $126.70  
  7 purchase totals = $1,191.28       $1,293.2262   $1,293.22   $1,293.25   $1,293.30