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 $92.28   8.541%   $100.1616   $100.16   $100.15   $100.20  
  Purchase #2 $226.73   9.423%   $248.0948   $248.09   $248.10   $248.10  
  Purchase #3 $168.76   4.477%   $176.3154   $176.32   $176.30   $176.30  
  Purchase #4 $103.57   10.703%   $114.6551   $114.66   $114.65   $114.70  
  Purchase #5 $132.95   12.486%   $149.5501   $149.55   $149.55   $149.60  
  Purchase #6 $53.52   13.165%   $60.5659   $60.57   $60.55   $60.60  
  Purchase #7 $150.68   9.423%   $164.8786   $164.88   $164.90   $164.90  
  7 purchase totals = $928.49       $1,014.2215   $1,014.23   $1,014.20   $1,014.40