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 $23.37   13.306%   $26.4796   $26.48   $26.50   $26.50  
  Purchase #2 $176.30   11.570%   $196.6979   $196.70   $196.70   $196.70  
  Purchase #3 $196.46   11.542%   $219.1354   $219.14   $219.15   $219.10  
  Purchase #4 $26.27   6.585%   $27.9999   $28.00   $28.00   $28.00  
  Purchase #5 $157.77   3.285%   $162.9527   $162.95   $162.95   $163.00  
  Purchase #6 $110.98   11.521%   $123.766   $123.77   $123.75   $123.80  
  Purchase #7 $185.36   10.760%   $205.3047   $205.30   $205.30   $205.30  
  7 purchase totals = $876.51       $962.3362   $962.34   $962.35   $962.40