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 $161.92   10.402%   $178.7629   $178.76   $178.75   $178.80  
  Purchase #2 $208.54   5.168%   $219.3173   $219.32   $219.30   $219.30  
  Purchase #3 $223.59   10.321%   $246.6667   $246.67   $246.65   $246.70  
  Purchase #4 $76.36   8.136%   $82.5726   $82.57   $82.55   $82.60  
  Purchase #5 $132.99   4.634%   $139.1528   $139.15   $139.15   $139.20  
  Purchase #6 $245.98   7.519%   $264.4752   $264.48   $264.50   $264.50  
  Purchase #7 $70.43   3.698%   $73.0345   $73.03   $73.05   $73.00  
  7 purchase totals = $1,119.81       $1,203.9820   $1,203.98   $1,203.95   $1,204.10