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 $119.94   3.672%   $124.3442   $124.34   $124.35   $124.30  
  Purchase #2 $111.51   3.622%   $115.5489   $115.55   $115.55   $115.50  
  Purchase #3 $153.51   6.606%   $163.6509   $163.65   $163.65   $163.70  
  Purchase #4 $192.95   12.759%   $217.5685   $217.57   $217.55   $217.60  
  Purchase #5 $209.43   10.794%   $232.0359   $232.04   $232.05   $232.00  
  Purchase #6 $236.99   4.389%   $247.3915   $247.39   $247.40   $247.40  
  Purchase #7 $94.84   10.554%   $104.8494   $104.85   $104.85   $104.80  
  7 purchase totals = $1,119.17       $1,205.3893   $1,205.39   $1,205.40   $1,205.30