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	$242.52	3.379%	$250.7148	$250.71	$250.70	$250.70
Purchase #2	$230.49	6.341%	$245.1054	$245.11	$245.10	$245.10
Purchase #3	$182.68	4.209%	$190.369	$190.37	$190.35	$190.40
Purchase #4	$154.52	7.673%	$166.3763	$166.38	$166.40	$166.40
Purchase #5	$46.91	8.671%	$50.9776	$50.98	$51.00	$51.00
Purchase #6	$84.73	7.227%	$90.8534	$90.85	$90.85	$90.90
Purchase #7	$170.59	4.857%	$178.8756	$178.88	$178.90	$178.90
7 purchase totals =	$1,112.44		$1,173.2721	$1,173.28	$1,173.30	$1,173.40