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 $56.42   5.555%   $59.5541   $59.55   $59.55   $59.60  
  Purchase #2 $210.93   8.557%   $228.9793   $228.98   $229.00   $229.00  
  Purchase #3 $192.77   11.368%   $214.6841   $214.68   $214.70   $214.70  
  Purchase #4 $67.54   6.562%   $71.972   $71.97   $71.95   $72.00  
  Purchase #5 $81.66   5.852%   $86.4387   $86.44   $86.45   $86.40  
  Purchase #6 $155.26   8.673%   $168.7257   $168.73   $168.75   $168.70  
  Purchase #7 $219.83   13.412%   $249.3136   $249.31   $249.30   $249.30  
  7 purchase totals = $984.41       $1,079.6675   $1,079.66   $1,079.70   $1,079.70