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 $55.36   10.276%   $61.0488   $61.05   $61.05   $61.00  
  Purchase #2 $249.97   12.630%   $281.5412   $281.54   $281.55   $281.50  
  Purchase #3 $92.54   6.747%   $98.7837   $98.78   $98.80   $98.80  
  Purchase #4 $192.62   11.544%   $214.8561   $214.86   $214.85   $214.90  
  Purchase #5 $37.31   9.489%   $40.8503   $40.85   $40.85   $40.90  
  Purchase #6 $96.53   8.844%   $105.0671   $105.07   $105.05   $105.10  
  Purchase #7 $241.28   4.618%   $252.4223   $252.42   $252.40   $252.40  
  7 purchase totals = $965.61       $1,054.5695   $1,054.57   $1,054.55   $1,054.60