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	$53.87	10.846%	$59.7127	$59.71	$59.70	$59.70
Purchase #2	$246.50	8.274%	$266.8954	$266.90	$266.90	$266.90
Purchase #3	$30.44	11.376%	$33.9029	$33.90	$33.90	$33.90
Purchase #4	$126.73	4.480%	$132.4075	$132.41	$132.40	$132.40
Purchase #5	$71.30	13.233%	$80.7351	$80.74	$80.75	$80.70
Purchase #6	$146.83	5.755%	$155.2801	$155.28	$155.30	$155.30
Purchase #7	$166.60	3.183%	$171.9029	$171.90	$171.90	$171.90
7 purchase totals =	$842.27		$900.8366	$900.84	$900.85	$900.80