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 $84.69   9.309%   $92.5738   $92.57   $92.55   $92.60  
  Purchase #2 $227.65   10.383%   $251.2869   $251.29   $251.30   $251.30  
  Purchase #3 $118.61   3.764%   $123.0745   $123.07   $123.05   $123.10  
  Purchase #4 $115.53   9.123%   $126.0698   $126.07   $126.05   $126.10  
  Purchase #5 $219.75   10.696%   $243.2545   $243.25   $243.25   $243.30  
  Purchase #6 $231.47   4.298%   $241.4186   $241.42   $241.40   $241.40  
  Purchase #7 $101.88   13.778%   $115.917   $115.92   $115.90   $115.90  
  7 purchase totals = $1,099.58       $1,193.5951   $1,193.59   $1,193.50   $1,193.70