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 $49.74   4.752%   $52.1036   $52.10   $52.10   $52.10  
  Purchase #2 $173.95   3.342%   $179.7634   $179.76   $179.75   $179.80  
  Purchase #3 $185.95   12.643%   $209.4597   $209.46   $209.45   $209.50  
  Purchase #4 $243.99   10.141%   $268.733   $268.73   $268.75   $268.70  
  Purchase #5 $240.76   7.402%   $258.5811   $258.58   $258.60   $258.60  
  Purchase #6 $212.92   6.699%   $227.1835   $227.18   $227.20   $227.20  
  Purchase #7 $170.99   9.189%   $186.7023   $186.70   $186.70   $186.70  
  7 purchase totals = $1,278.30       $1,382.5266   $1,382.51   $1,382.55   $1,382.60