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 $22.54   13.523%   $25.5881   $25.59   $25.60   $25.60  
  Purchase #2 $247.57   8.865%   $269.5171   $269.52   $269.50   $269.50  
  Purchase #3 $76.45   7.208%   $81.9605   $81.96   $81.95   $82.00  
  Purchase #4 $13.81   13.283%   $15.6444   $15.64   $15.65   $15.60  
  Purchase #5 $5.81   7.807%   $6.2636   $6.26   $6.25   $6.30  
  Purchase #6 $248.89   13.271%   $281.9202   $281.92   $281.90   $281.90  
  Purchase #7 $110.61   12.829%   $124.8002   $124.80   $124.80   $124.80  
  7 purchase totals = $725.68       $805.6941   $805.69   $805.65   $805.70