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 $59.54   6.622%   $63.4827   $63.48   $63.50   $63.50  
  Purchase #2 $27.44   6.694%   $29.2768   $29.28   $29.30   $29.30  
  Purchase #3 $113.54   6.696%   $121.1426   $121.14   $121.15   $121.10  
  Purchase #4 $62.29   6.871%   $66.5699   $66.57   $66.55   $66.60  
  Purchase #5 $124.64   12.460%   $140.1701   $140.17   $140.15   $140.20  
  Purchase #6 $15.45   8.437%   $16.7535   $16.75   $16.75   $16.80  
  Purchase #7 $56.41   7.144%   $60.4399   $60.44   $60.45   $60.40  
  7 purchase totals = $459.31       $497.8355   $497.83   $497.85   $497.90