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 $216.90   3.402%   $224.2789   $224.28   $224.30   $224.30  
  Purchase #2 $90.43   5.309%   $95.2309   $95.23   $95.25   $95.20  
  Purchase #3 $69.30   7.873%   $74.756   $74.76   $74.75   $74.80  
  Purchase #4 $24.45   6.484%   $26.0353   $26.04   $26.05   $26.00  
  Purchase #5 $53.49   6.144%   $56.7764   $56.78   $56.80   $56.80  
  Purchase #6 $102.80   12.499%   $115.649   $115.65   $115.65   $115.60  
  Purchase #7 $151.46   12.628%   $170.5864   $170.59   $170.60   $170.60  
  7 purchase totals = $708.83       $763.3129   $763.33   $763.40   $763.30