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 $93.98   5.194%   $98.8613   $98.86   $98.85   $98.90  
  Purchase #2 $107.78   6.408%   $114.6865   $114.69   $114.70   $114.70  
  Purchase #3 $249.49   7.871%   $269.1274   $269.13   $269.15   $269.10  
  Purchase #4 $124.78   5.159%   $131.2174   $131.22   $131.20   $131.20  
  Purchase #5 $173.75   7.223%   $186.3   $186.30   $186.30   $186.30  
  Purchase #6 $53.75   5.143%   $56.5144   $56.51   $56.50   $56.50  
  Purchase #7 $244.33   8.467%   $265.0174   $265.02   $265.00   $265.00  
  7 purchase totals = $1,047.86       $1,121.7244   $1,121.73   $1,121.70   $1,121.70