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 $240.65   7.869%   $259.5867   $259.59   $259.60   $259.60  
  Purchase #2 $71.96   4.170%   $74.9607   $74.96   $74.95   $75.00  
  Purchase #3 $126.75   5.170%   $133.303   $133.30   $133.30   $133.30  
  Purchase #4 $190.25   5.680%   $201.0562   $201.06   $201.05   $201.10  
  Purchase #5 $129.73   4.476%   $135.5367   $135.54   $135.55   $135.50  
  Purchase #6 $114.64   7.514%   $123.254   $123.25   $123.25   $123.30  
  Purchase #7 $239.27   7.228%   $256.5644   $256.56   $256.55   $256.60  
  7 purchase totals = $1,113.25       $1,184.2617   $1,184.26   $1,184.25   $1,184.40