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 $76.58   8.190%   $82.8519   $82.85   $82.85   $82.90  
  Purchase #2 $148.91   4.840%   $156.1172   $156.12   $156.10   $156.10  
  Purchase #3 $88.69   5.489%   $93.5582   $93.56   $93.55   $93.60  
  Purchase #4 $197.37   3.627%   $204.5286   $204.53   $204.55   $204.50  
  Purchase #5 $49.66   3.859%   $51.5764   $51.58   $51.60   $51.60  
  Purchase #6 $192.99   7.491%   $207.4469   $207.45   $207.45   $207.40  
  Purchase #7 $163.71   5.630%   $172.9269   $172.93   $172.95   $172.90  
  7 purchase totals = $917.91       $969.0061   $969.02   $969.05   $969.00