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	$36.35	10.498%	$40.166	$40.17	$40.15	$40.20
Purchase #2	$39.32	10.395%	$43.4073	$43.41	$43.40	$43.40
Purchase #3	$168.92	12.640%	$190.2715	$190.27	$190.25	$190.30
Purchase #4	$33.67	4.385%	$35.1464	$35.15	$35.15	$35.10
Purchase #5	$179.36	7.860%	$193.4577	$193.46	$193.45	$193.50
Purchase #6	$20.82	3.187%	$21.4835	$21.48	$21.50	$21.50
Purchase #7	$76.63	5.160%	$80.5841	$80.58	$80.60	$80.60
7 purchase totals =	$555.07		$604.5165	$604.52	$604.50	$604.60