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 $211.38   13.171%   $239.2209   $239.22   $239.20   $239.20  
  Purchase #2 $167.44   7.508%   $180.0114   $180.01   $180.00   $180.00  
  Purchase #3 $86.48   9.860%   $95.0069   $95.01   $95.00   $95.00  
  Purchase #4 $211.37   13.781%   $240.4989   $240.50   $240.50   $240.50  
  Purchase #5 $9.96   13.866%   $11.3411   $11.34   $11.35   $11.30  
  Purchase #6 $16.35   7.707%   $17.6101   $17.61   $17.60   $17.60  
  Purchase #7 $49.33   4.809%   $51.7023   $51.70   $51.70   $51.70  
  7 purchase totals = $752.31       $835.3916   $835.39   $835.35   $835.30