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 $63.42   5.492%   $66.903   $66.90   $66.90   $66.90  
  Purchase #2 $232.75   4.206%   $242.5395   $242.54   $242.55   $242.50  
  Purchase #3 $161.40   4.869%   $169.2586   $169.26   $169.25   $169.30  
  Purchase #4 $119.57   9.510%   $130.9411   $130.94   $130.95   $130.90  
  Purchase #5 $78.74   9.629%   $86.3219   $86.32   $86.30   $86.30  
  Purchase #6 $104.98   12.611%   $118.219   $118.22   $118.20   $118.20  
  Purchase #7 $79.92   6.527%   $85.1364   $85.14   $85.15   $85.10  
  7 purchase totals = $840.78       $899.3195   $899.32   $899.30   $899.20