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 $33.44   8.243%   $36.1965   $36.20   $36.20   $36.20  
  Purchase #2 $157.75   7.449%   $169.5008   $169.50   $169.50   $169.50  
  Purchase #3 $220.53   6.805%   $235.5371   $235.54   $235.55   $235.50  
  Purchase #4 $74.86   8.833%   $81.4724   $81.47   $81.45   $81.50  
  Purchase #5 $234.67   10.399%   $259.0733   $259.07   $259.05   $259.10  
  Purchase #6 $130.75   3.534%   $135.3707   $135.37   $135.35   $135.40  
  Purchase #7 $134.33   7.373%   $144.2342   $144.23   $144.25   $144.20  
  7 purchase totals = $986.33       $1,061.3850   $1,061.38   $1,061.35   $1,061.40