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	$135.69	10.661%	$150.1559	$150.16	$150.15	$150.20
Purchase #2	$52.32	3.490%	$54.146	$54.15	$54.15	$54.10
Purchase #3	$152.85	13.718%	$173.818	$173.82	$173.80	$173.80
Purchase #4	$19.47	6.422%	$20.7204	$20.72	$20.70	$20.70
Purchase #5	$114.49	3.488%	$118.4834	$118.48	$118.50	$118.50
Purchase #6	$223.41	7.874%	$241.0013	$241.00	$241.00	$241.00
Purchase #7	$226.56	7.660%	$243.9145	$243.91	$243.90	$243.90
7 purchase totals =	$924.79		$1,002.2395	$1,002.24	$1,002.20	$1,002.20