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 $108.63   12.702%   $122.4282   $122.43   $122.45   $122.40  
  Purchase #2 $207.53   12.677%   $233.8386   $233.84   $233.85   $233.80  
  Purchase #3 $157.29   9.576%   $172.3521   $172.35   $172.35   $172.40  
  Purchase #4 $139.86   8.839%   $152.2222   $152.22   $152.20   $152.20  
  Purchase #5 $176.58   11.841%   $197.4888   $197.49   $197.50   $197.50  
  Purchase #6 $125.66   9.487%   $137.5814   $137.58   $137.60   $137.60  
  Purchase #7 $237.55   5.233%   $249.981   $249.98   $250.00   $250.00  
  7 purchase totals = $1,153.10       $1,265.8923   $1,265.89   $1,265.95   $1,265.90