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 $116.25   13.574%   $132.0298   $132.03   $132.05   $132.00  
  Purchase #2 $47.75   8.121%   $51.6278   $51.63   $51.65   $51.60  
  Purchase #3 $116.74   12.322%   $131.1247   $131.12   $131.10   $131.10  
  Purchase #4 $45.96   5.456%   $48.4676   $48.47   $48.45   $48.50  
  Purchase #5 $233.70   12.146%   $262.0852   $262.09   $262.10   $262.10  
  Purchase #6 $250.32   13.607%   $284.381   $284.38   $284.40   $284.40  
  Purchase #7 $211.61   6.651%   $225.6842   $225.68   $225.70   $225.70  
  7 purchase totals = $1,022.33       $1,135.4003   $1,135.40   $1,135.45   $1,135.40