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	$6.65	9.315%	$7.2694	$7.27	$7.25	$7.30
Purchase #2	$161.69	5.850%	$171.1489	$171.15	$171.15	$171.10
Purchase #3	$136.41	6.633%	$145.4581	$145.46	$145.45	$145.50
Purchase #4	$122.57	9.752%	$134.523	$134.52	$134.50	$134.50
Purchase #5	$177.66	4.458%	$185.5801	$185.58	$185.60	$185.60
Purchase #6	$172.25	11.399%	$191.8848	$191.88	$191.90	$191.90
Purchase #7	$18.94	10.553%	$20.9387	$20.94	$20.95	$20.90
7 purchase totals =	$796.17		$856.8030	$856.80	$856.80	$856.80