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 $97.81   5.353%   $103.0458   $103.05   $103.05   $103.00  
  Purchase #2 $20.32   13.540%   $23.0713   $23.07   $23.05   $23.10  
  Purchase #3 $236.97   6.478%   $252.3209   $252.32   $252.30   $252.30  
  Purchase #4 $100.57   8.394%   $109.0118   $109.01   $109.00   $109.00  
  Purchase #5 $10.51   3.722%   $10.9012   $10.90   $10.90   $10.90  
  Purchase #6 $87.49   3.280%   $90.3597   $90.36   $90.35   $90.40  
  Purchase #7 $82.78   9.769%   $90.8668   $90.87   $90.85   $90.90  
  7 purchase totals = $636.45       $679.5775   $679.58   $679.50   $679.60