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 $183.26   6.611%   $195.3753   $195.38   $195.40   $195.40  
  Purchase #2 $86.32   12.543%   $97.1471   $97.15   $97.15   $97.10  
  Purchase #3 $184.82   10.801%   $204.7824   $204.78   $204.80   $204.80  
  Purchase #4 $151.41   10.646%   $167.5291   $167.53   $167.55   $167.50  
  Purchase #5 $68.59   11.175%   $76.2549   $76.25   $76.25   $76.30  
  Purchase #6 $240.39   8.320%   $260.3904   $260.39   $260.40   $260.40  
  Purchase #7 $246.99   3.366%   $255.3037   $255.30   $255.30   $255.30  
  7 purchase totals = $1,161.78       $1,256.7829   $1,256.78   $1,256.85   $1,256.80