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	$17.91	6.296%	$19.0376	$19.04	$19.05	$19.00
Purchase #2	$152.25	4.256%	$158.7298	$158.73	$158.75	$158.70
Purchase #3	$82.28	9.282%	$89.9172	$89.92	$89.90	$89.90
Purchase #4	$215.78	3.451%	$223.2266	$223.23	$223.25	$223.20
Purchase #5	$234.82	10.592%	$259.6921	$259.69	$259.70	$259.70
Purchase #6	$80.89	10.266%	$89.1942	$89.19	$89.20	$89.20
Purchase #7	$178.53	11.118%	$198.379	$198.38	$198.40	$198.40
7 purchase totals =	$962.46		$1,038.1765	$1,038.18	$1,038.25	$1,038.10