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 $236.75   13.175%   $267.9418   $267.94   $267.95   $267.90  
  Purchase #2 $116.64   12.311%   $130.9996   $131.00   $131.00   $131.00  
  Purchase #3 $52.82   10.720%   $58.4823   $58.48   $58.50   $58.50  
  Purchase #4 $55.64   4.140%   $57.9435   $57.94   $57.95   $57.90  
  Purchase #5 $107.74   12.276%   $120.9662   $120.97   $120.95   $121.00  
  Purchase #6 $248.96   6.632%   $265.471   $265.47   $265.45   $265.50  
  Purchase #7 $203.89   11.128%   $226.5789   $226.58   $226.60   $226.60  
  7 purchase totals = $1,022.44       $1,128.3833   $1,128.38   $1,128.40   $1,128.40