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 $23.31   11.462%   $25.9818   $25.98   $26.00   $26.00  
  Purchase #2 $192.90   4.123%   $200.8533   $200.85   $200.85   $200.90  
  Purchase #3 $23.90   13.842%   $27.2082   $27.21   $27.20   $27.20  
  Purchase #4 $179.41   4.457%   $187.4063   $187.41   $187.40   $187.40  
  Purchase #5 $123.29   9.668%   $135.2097   $135.21   $135.20   $135.20  
  Purchase #6 $79.48   4.382%   $82.9628   $82.96   $82.95   $83.00  
  Purchase #7 $224.89   12.221%   $252.3738   $252.37   $252.35   $252.40  
  7 purchase totals = $847.18       $911.9959   $911.99   $911.95   $912.10