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	$86.29	3.758%	$89.5328	$89.53	$89.55	$89.50
Purchase #2	$53.53	11.576%	$59.7266	$59.73	$59.75	$59.70
Purchase #3	$40.78	12.614%	$45.924	$45.92	$45.90	$45.90
Purchase #4	$156.77	3.783%	$162.7006	$162.70	$162.70	$162.70
Purchase #5	$100.47	4.639%	$105.1308	$105.13	$105.15	$105.10
Purchase #6	$62.54	12.394%	$70.2912	$70.29	$70.30	$70.30
Purchase #7	$228.72	11.529%	$255.0891	$255.09	$255.10	$255.10
7 purchase totals =	$729.10		$788.3951	$788.39	$788.45	$788.30