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 $77.56   11.271%   $86.3018   $86.30   $86.30   $86.30  
  Purchase #2 $90.61   4.567%   $94.7482   $94.75   $94.75   $94.70  
  Purchase #3 $159.91   4.233%   $166.679   $166.68   $166.70   $166.70  
  Purchase #4 $204.99   5.510%   $216.2849   $216.28   $216.30   $216.30  
  Purchase #5 $115.98   5.331%   $122.1629   $122.16   $122.15   $122.20  
  Purchase #6 $38.67   3.270%   $39.9345   $39.93   $39.95   $39.90  
  Purchase #7 $75.80   8.492%   $82.2369   $82.24   $82.25   $82.20  
  7 purchase totals = $763.52       $808.3482   $808.34   $808.40   $808.30