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	$213.75	13.228%	$242.0249	$242.02	$242.00	$242.00
Purchase #2	$90.73	9.266%	$99.137	$99.14	$99.15	$99.10
Purchase #3	$63.42	7.173%	$67.9691	$67.97	$67.95	$68.00
Purchase #4	$182.46	3.124%	$188.1601	$188.16	$188.15	$188.20
Purchase #5	$130.70	6.461%	$139.1445	$139.14	$139.15	$139.10
Purchase #6	$6.95	12.325%	$7.8066	$7.81	$7.80	$7.80
Purchase #7	$10.86	13.104%	$12.2831	$12.28	$12.30	$12.30
7 purchase totals =	$698.87		$756.5253	$756.52	$756.50	$756.50