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	$151.72	8.623%	$164.8028	$164.80	$164.80	$164.80
Purchase #2	$18.55	12.117%	$20.7977	$20.80	$20.80	$20.80
Purchase #3	$17.83	13.645%	$20.2629	$20.26	$20.25	$20.30
Purchase #4	$194.61	10.447%	$214.9409	$214.94	$214.95	$214.90
Purchase #5	$165.43	12.266%	$185.7216	$185.72	$185.70	$185.70
Purchase #6	$79.95	4.362%	$83.4374	$83.44	$83.45	$83.40
Purchase #7	$100.44	12.236%	$112.7298	$112.73	$112.75	$112.70
7 purchase totals =	$728.53		$802.6931	$802.69	$802.70	$802.60