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	$96.33	3.629%	$99.8258	$99.83	$99.85	$99.80
Purchase #2	$56.67	10.198%	$62.4492	$62.45	$62.45	$62.40
Purchase #3	$10.85	13.256%	$12.2883	$12.29	$12.30	$12.30
Purchase #4	$41.69	6.586%	$44.4357	$44.44	$44.45	$44.40
Purchase #5	$63.63	12.669%	$71.6913	$71.69	$71.70	$71.70
Purchase #6	$176.64	4.702%	$184.9456	$184.95	$184.95	$184.90
Purchase #7	$156.75	3.606%	$162.4024	$162.40	$162.40	$162.40
7 purchase totals =	$602.56		$638.0383	$638.05	$638.10	$637.90