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	$75.31	4.236%	$78.5001	$78.50	$78.50	$78.50
Purchase #2	$210.38	11.571%	$234.7231	$234.72	$234.70	$234.70
Purchase #3	$51.26	8.753%	$55.7468	$55.75	$55.75	$55.70
Purchase #4	$181.52	8.251%	$196.4972	$196.50	$196.50	$196.50
Purchase #5	$104.31	6.812%	$111.4156	$111.42	$111.40	$111.40
Purchase #6	$118.51	5.223%	$124.6998	$124.70	$124.70	$124.70
Purchase #7	$178.69	12.321%	$200.7064	$200.71	$200.70	$200.70
7 purchase totals =	$919.98		$1,002.2890	$1,002.30	$1,002.25	$1,002.20