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 $87.75   8.141%   $94.8937   $94.89   $94.90   $94.90  
  Purchase #2 $201.62   4.634%   $210.9631   $210.96   $210.95   $211.00  
  Purchase #3 $118.28   11.612%   $132.0147   $132.01   $132.00   $132.00  
  Purchase #4 $183.35   7.652%   $197.3799   $197.38   $197.40   $197.40  
  Purchase #5 $63.29   8.174%   $68.4633   $68.46   $68.45   $68.50  
  Purchase #6 $137.91   13.803%   $156.9457   $156.95   $156.95   $156.90  
  Purchase #7 $130.97   8.444%   $142.0291   $142.03   $142.05   $142.00  
  7 purchase totals = $923.17       $1,002.6895   $1,002.68   $1,002.70   $1,002.70