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 $229.54   13.727%   $261.049   $261.05   $261.05   $261.00  
  Purchase #2 $41.27   8.205%   $44.6562   $44.66   $44.65   $44.70  
  Purchase #3 $77.77   8.665%   $84.5088   $84.51   $84.50   $84.50  
  Purchase #4 $138.84   11.202%   $154.3929   $154.39   $154.40   $154.40  
  Purchase #5 $132.45   6.350%   $140.8606   $140.86   $140.85   $140.90  
  Purchase #6 $164.47   11.402%   $183.2229   $183.22   $183.20   $183.20  
  Purchase #7 $185.64   4.370%   $193.7525   $193.75   $193.75   $193.80  
  7 purchase totals = $969.98       $1,062.4429   $1,062.44   $1,062.40   $1,062.50