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 $82.39   13.656%   $93.6412   $93.64   $93.65   $93.60  
  Purchase #2 $146.34   10.430%   $161.6033   $161.60   $161.60   $161.60  
  Purchase #3 $206.44   11.603%   $230.3932   $230.39   $230.40   $230.40  
  Purchase #4 $98.45   9.685%   $107.9849   $107.98   $108.00   $108.00  
  Purchase #5 $79.74   13.385%   $90.4132   $90.41   $90.40   $90.40  
  Purchase #6 $86.55   4.728%   $90.6421   $90.64   $90.65   $90.60  
  Purchase #7 $77.96   5.210%   $82.0217   $82.02   $82.00   $82.00  
  7 purchase totals = $777.87       $856.6996   $856.68   $856.70   $856.60