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 $243.63   13.677%   $276.9513   $276.95   $276.95   $277.00  
  Purchase #2 $182.85   12.352%   $205.4356   $205.44   $205.45   $205.40  
  Purchase #3 $93.59   9.574%   $102.5503   $102.55   $102.55   $102.60  
  Purchase #4 $214.59   9.266%   $234.4739   $234.47   $234.45   $234.50  
  Purchase #5 $244.69   10.175%   $269.5872   $269.59   $269.60   $269.60  
  Purchase #6 $84.29   3.120%   $86.9198   $86.92   $86.90   $86.90  
  Purchase #7 $233.99   7.262%   $250.9824   $250.98   $251.00   $251.00  
  7 purchase totals = $1,297.63       $1,426.9005   $1,426.90   $1,426.90   $1,427.00