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 $78.71   10.469%   $86.9501   $86.95   $86.95   $87.00  
  Purchase #2 $69.25   9.190%   $75.6141   $75.61   $75.60   $75.60  
  Purchase #3 $114.34   4.864%   $119.9015   $119.90   $119.90   $119.90  
  Purchase #4 $115.60   10.584%   $127.8351   $127.84   $127.85   $127.80  
  Purchase #5 $206.26   9.540%   $225.9372   $225.94   $225.95   $225.90  
  Purchase #6 $64.41   13.588%   $73.162   $73.16   $73.15   $73.20  
  Purchase #7 $109.79   10.372%   $121.1774   $121.18   $121.20   $121.20  
  7 purchase totals = $758.36       $830.5774   $830.58   $830.60   $830.60