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 $204.67   6.648%   $218.2765   $218.28   $218.30   $218.30  
  Purchase #2 $225.79   5.705%   $238.6713   $238.67   $238.65   $238.70  
  Purchase #3 $119.63   8.637%   $129.9624   $129.96   $129.95   $130.00  
  Purchase #4 $227.85   6.322%   $242.2547   $242.25   $242.25   $242.30  
  Purchase #5 $31.53   5.364%   $33.2213   $33.22   $33.20   $33.20  
  Purchase #6 $230.48   7.707%   $248.2431   $248.24   $248.25   $248.20  
  Purchase #7 $93.96   10.543%   $103.8662   $103.87   $103.85   $103.90  
  7 purchase totals = $1,133.91       $1,214.4955   $1,214.49   $1,214.45   $1,214.60