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 $34.53   7.693%   $37.1864   $37.19   $37.20   $37.20  
  Purchase #2 $243.97   11.151%   $271.1751   $271.18   $271.20   $271.20  
  Purchase #3 $231.88   3.392%   $239.7454   $239.75   $239.75   $239.70  
  Purchase #4 $168.75   3.155%   $174.0741   $174.07   $174.05   $174.10  
  Purchase #5 $117.69   9.406%   $128.7599   $128.76   $128.75   $128.80  
  Purchase #6 $141.77   11.624%   $158.2493   $158.25   $158.25   $158.20  
  Purchase #7 $16.83   3.768%   $17.4642   $17.46   $17.45   $17.50  
  7 purchase totals = $955.42       $1,026.6544   $1,026.66   $1,026.65   $1,026.70