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	$59.71	9.122%	$65.1567	$65.16	$65.15	$65.20
Purchase #2	$231.55	6.370%	$246.2997	$246.30	$246.30	$246.30
Purchase #3	$139.92	8.206%	$151.4018	$151.40	$151.40	$151.40
Purchase #4	$7.26	3.399%	$7.5068	$7.51	$7.50	$7.50
Purchase #5	$195.92	7.420%	$210.4573	$210.46	$210.45	$210.50
Purchase #6	$139.43	3.439%	$144.225	$144.23	$144.25	$144.20
Purchase #7	$179.80	8.381%	$194.869	$194.87	$194.85	$194.90
7 purchase totals =	$953.59		$1,019.9163	$1,019.93	$1,019.90	$1,020.00