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 $77.55   11.494%   $86.4636   $86.46   $86.45   $86.50  
  Purchase #2 $166.62   11.458%   $185.7113   $185.71   $185.70   $185.70  
  Purchase #3 $160.98   10.756%   $178.295   $178.30   $178.30   $178.30  
  Purchase #4 $186.84   10.607%   $206.6581   $206.66   $206.65   $206.70  
  Purchase #5 $15.69   5.763%   $16.5942   $16.59   $16.60   $16.60  
  Purchase #6 $174.59   4.732%   $182.8516   $182.85   $182.85   $182.90  
  Purchase #7 $143.35   10.518%   $158.4276   $158.43   $158.45   $158.40  
  7 purchase totals = $925.62       $1,015.0014   $1,015.00   $1,015.00   $1,015.10