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 $24.35   10.390%   $26.88   $26.88   $26.90   $26.90  
  Purchase #2 $105.99   6.247%   $112.6112   $112.61   $112.60   $112.60  
  Purchase #3 $142.77   11.359%   $158.9872   $158.99   $159.00   $159.00  
  Purchase #4 $61.67   12.728%   $69.5194   $69.52   $69.50   $69.50  
  Purchase #5 $248.56   7.330%   $266.7794   $266.78   $266.80   $266.80  
  Purchase #6 $158.36   4.747%   $165.8773   $165.88   $165.90   $165.90  
  Purchase #7 $194.32   11.571%   $216.8048   $216.80   $216.80   $216.80  
  7 purchase totals = $936.02       $1,017.4593   $1,017.46   $1,017.50   $1,017.50