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 $204.26   9.723%   $224.1202   $224.12   $224.10   $224.10  
  Purchase #2 $123.69   9.548%   $135.4999   $135.50   $135.50   $135.50  
  Purchase #3 $144.83   13.790%   $164.8021   $164.80   $164.80   $164.80  
  Purchase #4 $236.99   4.200%   $246.9436   $246.94   $246.95   $246.90  
  Purchase #5 $31.50   12.630%   $35.4785   $35.48   $35.50   $35.50  
  Purchase #6 $151.99   9.350%   $166.2011   $166.20   $166.20   $166.20  
  Purchase #7 $46.83   7.114%   $50.1615   $50.16   $50.15   $50.20  
  7 purchase totals = $940.09       $1,023.2069   $1,023.20   $1,023.20   $1,023.20