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 $92.61   9.734%   $101.6247   $101.62   $101.60   $101.60  
  Purchase #2 $125.28   6.242%   $133.1   $133.10   $133.10   $133.10  
  Purchase #3 $167.56   3.125%   $172.7963   $172.80   $172.80   $172.80  
  Purchase #4 $93.32   13.367%   $105.7941   $105.79   $105.80   $105.80  
  Purchase #5 $19.58   13.249%   $22.1742   $22.17   $22.15   $22.20  
  Purchase #6 $245.67   8.534%   $266.6355   $266.64   $266.65   $266.60  
  Purchase #7 $214.30   10.161%   $236.075   $236.08   $236.10   $236.10  
  7 purchase totals = $958.32       $1,038.1998   $1,038.20   $1,038.20   $1,038.20