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 $196.69   11.844%   $219.986   $219.99   $220.00   $220.00  
  Purchase #2 $97.58   7.759%   $105.1512   $105.15   $105.15   $105.20  
  Purchase #3 $105.94   13.507%   $120.2493   $120.25   $120.25   $120.20  
  Purchase #4 $208.26   5.509%   $219.733   $219.73   $219.75   $219.70  
  Purchase #5 $131.69   11.505%   $146.8409   $146.84   $146.85   $146.80  
  Purchase #6 $233.89   3.599%   $242.3077   $242.31   $242.30   $242.30  
  Purchase #7 $134.91   9.594%   $147.8533   $147.85   $147.85   $147.90  
  7 purchase totals = $1,108.96       $1,202.1214   $1,202.12   $1,202.15   $1,202.10