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 $176.55   5.230%   $185.7836   $185.78   $185.80   $185.80  
  Purchase #2 $121.71   10.319%   $134.2693   $134.27   $134.25   $134.30  
  Purchase #3 $158.55   4.851%   $166.2413   $166.24   $166.25   $166.20  
  Purchase #4 $189.77   8.233%   $205.3938   $205.39   $205.40   $205.40  
  Purchase #5 $213.86   10.233%   $235.7443   $235.74   $235.75   $235.70  
  Purchase #6 $206.50   5.427%   $217.7068   $217.71   $217.70   $217.70  
  Purchase #7 $53.60   6.106%   $56.8728   $56.87   $56.85   $56.90  
  7 purchase totals = $1,120.54       $1,202.0119   $1,202.00   $1,202.00   $1,202.00