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 $147.36   12.311%   $165.5015   $165.50   $165.50   $165.50  
  Purchase #2 $208.59   3.660%   $216.2244   $216.22   $216.20   $216.20  
  Purchase #3 $116.97   6.635%   $124.731   $124.73   $124.75   $124.70  
  Purchase #4 $241.77   13.109%   $273.4636   $273.46   $273.45   $273.50  
  Purchase #5 $85.29   10.265%   $94.045   $94.05   $94.05   $94.00  
  Purchase #6 $36.41   11.646%   $40.6503   $40.65   $40.65   $40.70  
  Purchase #7 $233.62   7.639%   $251.4662   $251.47   $251.45   $251.50  
  7 purchase totals = $1,070.01       $1,166.0820   $1,166.08   $1,166.05   $1,166.10