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 $61.81   11.675%   $69.0263   $69.03   $69.05   $69.00  
  Purchase #2 $154.34   7.240%   $165.5142   $165.51   $165.50   $165.50  
  Purchase #3 $94.50   7.739%   $101.8134   $101.81   $101.80   $101.80  
  Purchase #4 $248.88   12.420%   $279.7909   $279.79   $279.80   $279.80  
  Purchase #5 $194.70   10.152%   $214.4659   $214.47   $214.45   $214.50  
  Purchase #6 $28.59   5.461%   $30.1513   $30.15   $30.15   $30.20  
  Purchase #7 $123.32   9.747%   $135.34   $135.34   $135.35   $135.30  
  7 purchase totals = $906.14       $996.1020   $996.10   $996.10   $996.10