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 $41.85   13.532%   $47.5131   $47.51   $47.50   $47.50  
  Purchase #2 $188.28   3.730%   $195.3028   $195.30   $195.30   $195.30  
  Purchase #3 $90.61   8.816%   $98.5982   $98.60   $98.60   $98.60  
  Purchase #4 $110.83   4.455%   $115.7675   $115.77   $115.75   $115.80  
  Purchase #5 $232.49   6.619%   $247.8785   $247.88   $247.90   $247.90  
  Purchase #6 $124.61   5.136%   $131.01   $131.01   $131.00   $131.00  
  Purchase #7 $249.53   3.332%   $257.8443   $257.84   $257.85   $257.80  
  7 purchase totals = $1,038.20       $1,093.9144   $1,093.91   $1,093.90   $1,093.90