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 $13.36   8.416%   $14.4844   $14.48   $14.50   $14.50  
  Purchase #2 $17.74   8.558%   $19.2582   $19.26   $19.25   $19.30  
  Purchase #3 $41.42   10.740%   $45.8685   $45.87   $45.85   $45.90  
  Purchase #4 $28.47   3.822%   $29.5581   $29.56   $29.55   $29.60  
  Purchase #5 $22.69   4.657%   $23.7467   $23.75   $23.75   $23.70  
  Purchase #6 $110.43   13.639%   $125.4915   $125.49   $125.50   $125.50  
  Purchase #7 $181.33   5.137%   $190.6449   $190.64   $190.65   $190.60  
  7 purchase totals = $415.44       $449.0523   $449.05   $449.05   $449.10