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 $206.73   9.574%   $226.5223   $226.52   $226.50   $226.50  
  Purchase #2 $166.84   10.256%   $183.9511   $183.95   $183.95   $184.00  
  Purchase #3 $87.29   8.338%   $94.5682   $94.57   $94.55   $94.60  
  Purchase #4 $206.41   6.311%   $219.4365   $219.44   $219.45   $219.40  
  Purchase #5 $239.35   9.202%   $261.375   $261.38   $261.40   $261.40  
  Purchase #6 $149.90   11.727%   $167.4788   $167.48   $167.50   $167.50  
  Purchase #7 $132.32   7.772%   $142.6039   $142.60   $142.60   $142.60  
  7 purchase totals = $1,188.84       $1,295.9358   $1,295.94   $1,295.95   $1,296.00