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 $243.87   4.256%   $254.2491   $254.25   $254.25   $254.20  
  Purchase #2 $111.80   3.431%   $115.6359   $115.64   $115.65   $115.60  
  Purchase #3 $29.36   8.268%   $31.7875   $31.79   $31.80   $31.80  
  Purchase #4 $124.95   10.661%   $138.2709   $138.27   $138.25   $138.30  
  Purchase #5 $102.50   12.710%   $115.5278   $115.53   $115.55   $115.50  
  Purchase #6 $158.76   12.258%   $178.2208   $178.22   $178.20   $178.20  
  Purchase #7 $82.63   3.550%   $85.5634   $85.56   $85.55   $85.60  
  7 purchase totals = $853.87       $919.2554   $919.26   $919.25   $919.20