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 $167.35   11.721%   $186.9651   $186.97   $186.95   $187.00  
  Purchase #2 $61.58   5.147%   $64.7495   $64.75   $64.75   $64.70  
  Purchase #3 $8.92   4.769%   $9.3454   $9.35   $9.35   $9.30  
  Purchase #4 $88.40   11.580%   $98.6367   $98.64   $98.65   $98.60  
  Purchase #5 $207.30   11.423%   $230.9799   $230.98   $231.00   $231.00  
  Purchase #6 $139.63   3.288%   $144.221   $144.22   $144.20   $144.20  
  Purchase #7 $214.30   6.652%   $228.5552   $228.56   $228.55   $228.60  
  7 purchase totals = $887.48       $963.4528   $963.47   $963.45   $963.40