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 $110.84   9.395%   $121.2534   $121.25   $121.25   $121.30  
  Purchase #2 $248.65   9.141%   $271.3791   $271.38   $271.40   $271.40  
  Purchase #3 $25.77   5.668%   $27.2306   $27.23   $27.25   $27.20  
  Purchase #4 $192.39   9.687%   $211.0268   $211.03   $211.05   $211.00  
  Purchase #5 $109.70   4.737%   $114.8965   $114.90   $114.90   $114.90  
  Purchase #6 $31.48   10.295%   $34.7209   $34.72   $34.70   $34.70  
  Purchase #7 $40.59   13.171%   $45.9361   $45.94   $45.95   $45.90  
  7 purchase totals = $759.42       $826.4434   $826.45   $826.50   $826.40