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	$80.65	3.222%	$83.2485	$83.25	$83.25	$83.20
Purchase #2	$142.25	12.766%	$160.4096	$160.41	$160.40	$160.40
Purchase #3	$128.64	12.849%	$145.169	$145.17	$145.15	$145.20
Purchase #4	$82.77	9.719%	$90.8144	$90.81	$90.80	$90.80
Purchase #5	$220.90	6.679%	$235.6539	$235.65	$235.65	$235.70
Purchase #6	$192.85	11.637%	$215.292	$215.29	$215.30	$215.30
Purchase #7	$83.88	5.596%	$88.5739	$88.57	$88.55	$88.60
7 purchase totals =	$931.94		$1,019.1613	$1,019.15	$1,019.10	$1,019.20