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	$64.39	3.178%	$66.4363	$66.44	$66.45	$66.40
Purchase #2	$122.69	12.346%	$137.8373	$137.84	$137.85	$137.80
Purchase #3	$53.72	6.865%	$57.4079	$57.41	$57.40	$57.40
Purchase #4	$148.62	5.160%	$156.2888	$156.29	$156.30	$156.30
Purchase #5	$28.48	10.794%	$31.5541	$31.55	$31.55	$31.60
Purchase #6	$20.98	8.109%	$22.6813	$22.68	$22.70	$22.70
Purchase #7	$72.85	13.512%	$82.6935	$82.69	$82.70	$82.70
7 purchase totals =	$511.73		$554.8992	$554.90	$554.95	$554.90