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	$25.33	13.496%	$28.7485	$28.75	$28.75	$28.70
Purchase #2	$156.66	5.517%	$165.3029	$165.30	$165.30	$165.30
Purchase #3	$173.47	10.188%	$191.1431	$191.14	$191.15	$191.10
Purchase #4	$128.46	6.385%	$136.6622	$136.66	$136.65	$136.70
Purchase #5	$140.46	12.787%	$158.4206	$158.42	$158.40	$158.40
Purchase #6	$41.69	4.245%	$43.4597	$43.46	$43.45	$43.50
Purchase #7	$34.51	4.782%	$36.1603	$36.16	$36.15	$36.20
7 purchase totals =	$700.58		$759.8973	$759.89	$759.85	$759.90