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 $72.82   3.794%   $75.5828   $75.58   $75.60   $75.60  
  Purchase #2 $218.81   10.709%   $242.2424   $242.24   $242.25   $242.20  
  Purchase #3 $192.34   7.106%   $206.0077   $206.01   $206.00   $206.00  
  Purchase #4 $154.49   4.102%   $160.8272   $160.83   $160.85   $160.80  
  Purchase #5 $211.69   7.244%   $227.0248   $227.02   $227.00   $227.00  
  Purchase #6 $141.91   9.839%   $155.8725   $155.87   $155.85   $155.90  
  Purchase #7 $234.87   12.333%   $263.8365   $263.84   $263.85   $263.80  
  7 purchase totals = $1,226.93       $1,331.3939   $1,331.39   $1,331.40   $1,331.30