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	$67.76	12.383%	$76.1507	$76.15	$76.15	$76.20
Purchase #2	$109.87	13.682%	$124.9024	$124.90	$124.90	$124.90
Purchase #3	$122.88	3.765%	$127.5064	$127.51	$127.50	$127.50
Purchase #4	$16.93	11.466%	$18.8712	$18.87	$18.85	$18.90
Purchase #5	$45.91	5.311%	$48.3483	$48.35	$48.35	$48.30
Purchase #6	$179.41	9.369%	$196.2189	$196.22	$196.20	$196.20
Purchase #7	$126.94	13.193%	$143.6872	$143.69	$143.70	$143.70
7 purchase totals =	$669.70		$735.6851	$735.69	$735.65	$735.70