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	$139.91	12.791%	$157.8059	$157.81	$157.80	$157.80
Purchase #2	$137.74	3.298%	$142.2827	$142.28	$142.30	$142.30
Purchase #3	$183.34	4.581%	$191.7388	$191.74	$191.75	$191.70
Purchase #4	$39.45	7.281%	$42.3224	$42.32	$42.30	$42.30
Purchase #5	$162.39	6.201%	$172.4598	$172.46	$172.45	$172.50
Purchase #6	$133.63	3.122%	$137.8019	$137.80	$137.80	$137.80
Purchase #7	$178.64	5.827%	$189.0494	$189.05	$189.05	$189.00
7 purchase totals =	$975.10		$1,033.4609	$1,033.46	$1,033.45	$1,033.40