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 $174.66   6.451%   $185.9273   $185.93   $185.95   $185.90  
  Purchase #2 $228.97   9.868%   $251.5648   $251.56   $251.55   $251.60  
  Purchase #3 $127.74   3.850%   $132.658   $132.66   $132.65   $132.70  
  Purchase #4 $250.55   9.781%   $275.0563   $275.06   $275.05   $275.10  
  Purchase #5 $237.51   5.261%   $250.0054   $250.01   $250.00   $250.00  
  Purchase #6 $238.69   13.859%   $271.77   $271.77   $271.75   $271.80  
  Purchase #7 $47.51   7.193%   $50.9274   $50.93   $50.95   $50.90  
  7 purchase totals = $1,305.63       $1,417.9092   $1,417.92   $1,417.90   $1,418.00