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 $201.98   4.128%   $210.3177   $210.32   $210.30   $210.30  
  Purchase #2 $114.42   4.439%   $119.4991   $119.50   $119.50   $119.50  
  Purchase #3 $168.56   7.290%   $180.848   $180.85   $180.85   $180.80  
  Purchase #4 $246.79   10.779%   $273.3915   $273.39   $273.40   $273.40  
  Purchase #5 $105.34   12.624%   $118.6381   $118.64   $118.65   $118.60  
  Purchase #6 $71.57   12.834%   $80.7553   $80.76   $80.75   $80.80  
  Purchase #7 $119.97   11.287%   $133.511   $133.51   $133.50   $133.50  
  7 purchase totals = $1,028.63       $1,116.9607   $1,116.97   $1,116.95   $1,116.90