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	$137.52	13.855%	$156.5734	$156.57	$156.55	$156.60
Purchase #2	$149.78	9.862%	$164.5513	$164.55	$164.55	$164.60
Purchase #3	$169.59	10.583%	$187.5377	$187.54	$187.55	$187.50
Purchase #4	$165.43	13.280%	$187.3991	$187.40	$187.40	$187.40
Purchase #5	$119.86	3.540%	$124.103	$124.10	$124.10	$124.10
Purchase #6	$196.28	13.807%	$223.3804	$223.38	$223.40	$223.40
Purchase #7	$54.90	3.650%	$56.9039	$56.90	$56.90	$56.90
7 purchase totals =	$993.36		$1,100.4488	$1,100.44	$1,100.45	$1,100.50