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	$244.98	13.487%	$278.0205	$278.02	$278.00	$278.00
Purchase #2	$85.42	4.333%	$89.1212	$89.12	$89.10	$89.10
Purchase #3	$141.88	5.514%	$149.7033	$149.70	$149.70	$149.70
Purchase #4	$90.28	11.428%	$100.5972	$100.60	$100.60	$100.60
Purchase #5	$135.25	9.430%	$148.0041	$148.00	$148.00	$148.00
Purchase #6	$141.88	6.289%	$150.8028	$150.80	$150.80	$150.80
Purchase #7	$67.38	4.488%	$70.404	$70.40	$70.40	$70.40
7 purchase totals =	$907.07		$986.6531	$986.64	$986.60	$986.60