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 $168.49   8.783%   $183.2885   $183.29   $183.30   $183.30  
  Purchase #2 $114.25   5.369%   $120.3841   $120.38   $120.40   $120.40  
  Purchase #3 $215.89   8.452%   $234.137   $234.14   $234.15   $234.10  
  Purchase #4 $231.39   4.455%   $241.6984   $241.70   $241.70   $241.70  
  Purchase #5 $115.76   12.353%   $130.0598   $130.06   $130.05   $130.10  
  Purchase #6 $170.57   3.558%   $176.6389   $176.64   $176.65   $176.60  
  Purchase #7 $28.43   5.379%   $29.9592   $29.96   $29.95   $30.00  
  7 purchase totals = $1,044.78       $1,116.1659   $1,116.17   $1,116.20   $1,116.20