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 $213.65   13.151%   $241.7471   $241.75   $241.75   $241.70  
  Purchase #2 $94.28   4.740%   $98.7489   $98.75   $98.75   $98.70  
  Purchase #3 $171.89   7.483%   $184.7525   $184.75   $184.75   $184.80  
  Purchase #4 $148.53   8.356%   $160.9412   $160.94   $160.95   $160.90  
  Purchase #5 $146.66   8.298%   $158.8298   $158.83   $158.85   $158.80  
  Purchase #6 $246.40   6.244%   $261.7852   $261.79   $261.80   $261.80  
  Purchase #7 $63.47   3.144%   $65.4655   $65.47   $65.45   $65.50  
  7 purchase totals = $1,084.88       $1,172.2702   $1,172.28   $1,172.30   $1,172.20