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	$50.46	5.613%	$53.2923	$53.29	$53.30	$53.30
Purchase #2	$165.62	10.685%	$183.3165	$183.32	$183.30	$183.30
Purchase #3	$145.30	7.401%	$156.0537	$156.05	$156.05	$156.10
Purchase #4	$36.47	12.282%	$40.9492	$40.95	$40.95	$40.90
Purchase #5	$118.61	7.544%	$127.5579	$127.56	$127.55	$127.60
Purchase #6	$105.39	6.401%	$112.136	$112.14	$112.15	$112.10
Purchase #7	$150.99	11.540%	$168.4142	$168.41	$168.40	$168.40
7 purchase totals =	$772.84		$841.7198	$841.72	$841.70	$841.70