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 $20.88   4.286%   $21.7749   $21.77   $21.75   $21.80  
  Purchase #2 $92.94   13.763%   $105.7313   $105.73   $105.75   $105.70  
  Purchase #3 $121.87   7.183%   $130.6239   $130.62   $130.60   $130.60  
  Purchase #4 $225.51   5.337%   $237.5455   $237.55   $237.55   $237.50  
  Purchase #5 $234.32   10.310%   $258.4784   $258.48   $258.50   $258.50  
  Purchase #6 $234.28   10.428%   $258.7107   $258.71   $258.70   $258.70  
  Purchase #7 $172.95   9.163%   $188.7974   $188.80   $188.80   $188.80  
  7 purchase totals = $1,102.75       $1,201.6621   $1,201.66   $1,201.65   $1,201.60