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 $247.74   4.641%   $259.2376   $259.24   $259.25   $259.20  
  Purchase #2 $227.37   11.448%   $253.3993   $253.40   $253.40   $253.40  
  Purchase #3 $165.66   3.776%   $171.9153   $171.92   $171.90   $171.90  
  Purchase #4 $84.73   12.469%   $95.295   $95.30   $95.30   $95.30  
  Purchase #5 $189.76   6.124%   $201.3809   $201.38   $201.40   $201.40  
  Purchase #6 $81.29   3.849%   $84.4189   $84.42   $84.40   $84.40  
  Purchase #7 $124.40   4.670%   $130.2095   $130.21   $130.20   $130.20  
  7 purchase totals = $1,120.95       $1,195.8565   $1,195.87   $1,195.85   $1,195.80