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	$198.94	6.422%	$211.7159	$211.72	$211.70	$211.70
Purchase #2	$187.33	12.491%	$210.7294	$210.73	$210.75	$210.70
Purchase #3	$49.46	6.197%	$52.525	$52.53	$52.55	$52.50
Purchase #4	$158.35	6.335%	$168.3815	$168.38	$168.40	$168.40
Purchase #5	$96.58	9.503%	$105.758	$105.76	$105.75	$105.80
Purchase #6	$71.71	11.575%	$80.0104	$80.01	$80.00	$80.00
Purchase #7	$36.35	13.604%	$41.2951	$41.30	$41.30	$41.30
7 purchase totals =	$798.72		$870.4153	$870.43	$870.45	$870.40