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	$77.74	7.314%	$83.4259	$83.43	$83.45	$83.40
Purchase #2	$162.90	6.851%	$174.0603	$174.06	$174.05	$174.10
Purchase #3	$191.43	9.559%	$209.7288	$209.73	$209.75	$209.70
Purchase #4	$163.85	5.170%	$172.321	$172.32	$172.30	$172.30
Purchase #5	$72.57	3.197%	$74.8901	$74.89	$74.90	$74.90
Purchase #6	$104.80	6.679%	$111.7996	$111.80	$111.80	$111.80
Purchase #7	$172.67	12.575%	$194.3833	$194.38	$194.40	$194.40
7 purchase totals =	$945.96		$1,020.6090	$1,020.61	$1,020.65	$1,020.60