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 $84.68   11.793%   $94.6663   $94.67   $94.65   $94.70  
  Purchase #2 $110.57   8.448%   $119.911   $119.91   $119.90   $119.90  
  Purchase #3 $59.89   13.396%   $67.9129   $67.91   $67.90   $67.90  
  Purchase #4 $98.89   3.303%   $102.1563   $102.16   $102.15   $102.20  
  Purchase #5 $175.45   9.830%   $192.6967   $192.70   $192.70   $192.70  
  Purchase #6 $67.78   6.748%   $72.3538   $72.35   $72.35   $72.40  
  Purchase #7 $233.67   10.656%   $258.5699   $258.57   $258.55   $258.60  
  7 purchase totals = $830.93       $908.2669   $908.27   $908.20   $908.40