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	$75.87	5.606%	$80.1233	$80.12	$80.10	$80.10
Purchase #2	$165.52	4.611%	$173.1521	$173.15	$173.15	$173.20
Purchase #3	$232.44	4.336%	$242.5186	$242.52	$242.50	$242.50
Purchase #4	$52.72	4.612%	$55.1514	$55.15	$55.15	$55.20
Purchase #5	$41.79	11.411%	$46.5587	$46.56	$46.55	$46.60
Purchase #6	$95.50	4.119%	$99.4336	$99.43	$99.45	$99.40
Purchase #7	$55.67	9.477%	$60.9458	$60.95	$60.95	$60.90
7 purchase totals =	$719.51		$757.8835	$757.88	$757.85	$757.90