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	$93.29	11.160%	$103.7012	$103.70	$103.70	$103.70
Purchase #2	$80.63	11.762%	$90.1137	$90.11	$90.10	$90.10
Purchase #3	$178.99	7.183%	$191.8469	$191.85	$191.85	$191.80
Purchase #4	$178.80	10.832%	$198.1676	$198.17	$198.15	$198.20
Purchase #5	$25.42	13.465%	$28.8428	$28.84	$28.85	$28.80
Purchase #6	$96.32	3.419%	$99.6132	$99.61	$99.60	$99.60
Purchase #7	$122.95	13.435%	$139.4683	$139.47	$139.45	$139.50
7 purchase totals =	$776.40		$851.7537	$851.75	$851.70	$851.70