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	$59.51	13.132%	$67.3249	$67.32	$67.30	$67.30
Purchase #2	$52.85	13.849%	$60.1692	$60.17	$60.15	$60.20
Purchase #3	$162.80	12.728%	$183.5212	$183.52	$183.50	$183.50
Purchase #4	$99.29	3.793%	$103.0561	$103.06	$103.05	$103.10
Purchase #5	$81.41	9.470%	$89.1195	$89.12	$89.10	$89.10
Purchase #6	$203.92	11.860%	$228.1049	$228.10	$228.10	$228.10
Purchase #7	$206.49	4.394%	$215.5632	$215.56	$215.55	$215.60
7 purchase totals =	$866.27		$946.8590	$946.85	$946.75	$946.90