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 $174.42   9.871%   $191.637   $191.64   $191.65   $191.60  
  Purchase #2 $227.81   13.820%   $259.2933   $259.29   $259.30   $259.30  
  Purchase #3 $207.91   4.772%   $217.8315   $217.83   $217.85   $217.80  
  Purchase #4 $133.40   8.506%   $144.747   $144.75   $144.75   $144.70  
  Purchase #5 $58.44   7.648%   $62.9095   $62.91   $62.90   $62.90  
  Purchase #6 $91.75   9.766%   $100.7103   $100.71   $100.70   $100.70  
  Purchase #7 $203.66   5.483%   $214.8267   $214.83   $214.85   $214.80  
  7 purchase totals = $1,097.39       $1,191.9553   $1,191.96   $1,192.00   $1,191.80