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	$80.87	13.175%	$91.5246	$91.52	$91.50	$91.50
Purchase #2	$106.56	11.441%	$118.7515	$118.75	$118.75	$118.80
Purchase #3	$220.36	3.535%	$228.1497	$228.15	$228.15	$228.10
Purchase #4	$215.48	12.295%	$241.9733	$241.97	$241.95	$242.00
Purchase #5	$105.28	6.107%	$111.7094	$111.71	$111.70	$111.70
Purchase #6	$120.89	11.772%	$135.1212	$135.12	$135.10	$135.10
Purchase #7	$99.85	3.597%	$103.4416	$103.44	$103.45	$103.40
7 purchase totals =	$949.29		$1,030.6713	$1,030.66	$1,030.60	$1,030.60