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 $248.97   8.130%   $269.2113   $269.21   $269.20   $269.20  
  Purchase #2 $42.69   13.551%   $48.4749   $48.47   $48.45   $48.50  
  Purchase #3 $56.96   3.540%   $58.9764   $58.98   $59.00   $59.00  
  Purchase #4 $148.86   8.845%   $162.0267   $162.03   $162.05   $162.00  
  Purchase #5 $224.93   4.397%   $234.8202   $234.82   $234.80   $234.80  
  Purchase #6 $88.64   4.609%   $92.7254   $92.73   $92.75   $92.70  
  Purchase #7 $157.56   4.696%   $164.959   $164.96   $164.95   $165.00  
  7 purchase totals = $968.61       $1,031.1939   $1,031.20   $1,031.20   $1,031.20