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 $82.34   13.516%   $93.4691   $93.47   $93.45   $93.50  
  Purchase #2 $225.64   12.414%   $253.6509   $253.65   $253.65   $253.70  
  Purchase #3 $89.63   3.774%   $93.0126   $93.01   $93.00   $93.00  
  Purchase #4 $5.35   3.208%   $5.5216   $5.52   $5.50   $5.50  
  Purchase #5 $51.89   12.195%   $58.218   $58.22   $58.20   $58.20  
  Purchase #6 $214.61   5.770%   $226.993   $226.99   $227.00   $227.00  
  Purchase #7 $22.48   5.390%   $23.6917   $23.69   $23.70   $23.70  
  7 purchase totals = $691.94       $754.5569   $754.55   $754.50   $754.60