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 $28.57   4.108%   $29.7437   $29.74   $29.75   $29.70  
  Purchase #2 $164.88   4.374%   $172.0919   $172.09   $172.10   $172.10  
  Purchase #3 $17.95   7.636%   $19.3207   $19.32   $19.30   $19.30  
  Purchase #4 $135.59   5.516%   $143.0691   $143.07   $143.05   $143.10  
  Purchase #5 $194.34   12.652%   $218.9279   $218.93   $218.95   $218.90  
  Purchase #6 $36.37   12.211%   $40.8111   $40.81   $40.80   $40.80  
  Purchase #7 $76.64   3.325%   $79.1883   $79.19   $79.20   $79.20  
  7 purchase totals = $654.34       $703.1527   $703.15   $703.15   $703.10