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 $243.83   4.662%   $255.1974   $255.20   $255.20   $255.20  
  Purchase #2 $18.44   12.742%   $20.7896   $20.79   $20.80   $20.80  
  Purchase #3 $165.31   5.199%   $173.9045   $173.90   $173.90   $173.90  
  Purchase #4 $201.34   13.217%   $227.9511   $227.95   $227.95   $228.00  
  Purchase #5 $201.55   6.252%   $214.1509   $214.15   $214.15   $214.20  
  Purchase #6 $175.90   5.238%   $185.1136   $185.11   $185.10   $185.10  
  Purchase #7 $157.59   12.433%   $177.1832   $177.18   $177.20   $177.20  
  7 purchase totals = $1,163.96       $1,254.2903   $1,254.28   $1,254.30   $1,254.40