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	$35.51	6.766%	$37.9126	$37.91	$37.90	$37.90
Purchase #2	$179.61	3.371%	$185.6647	$185.66	$185.65	$185.70
Purchase #3	$62.80	11.475%	$70.0063	$70.01	$70.00	$70.00
Purchase #4	$51.58	13.471%	$58.5283	$58.53	$58.55	$58.50
Purchase #5	$107.84	3.142%	$111.2283	$111.23	$111.25	$111.20
Purchase #6	$23.47	8.282%	$25.4138	$25.41	$25.40	$25.40
Purchase #7	$79.62	8.772%	$86.6043	$86.60	$86.60	$86.60
7 purchase totals =	$540.43		$575.3583	$575.35	$575.35	$575.30