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	$65.31	5.351%	$68.8047	$68.80	$68.80	$68.80
Purchase #2	$30.56	5.453%	$32.2264	$32.23	$32.25	$32.20
Purchase #3	$191.89	4.253%	$200.0511	$200.05	$200.05	$200.10
Purchase #4	$51.89	8.208%	$56.1491	$56.15	$56.15	$56.10
Purchase #5	$158.64	13.754%	$180.4593	$180.46	$180.45	$180.50
Purchase #6	$27.40	3.371%	$28.3237	$28.32	$28.30	$28.30
Purchase #7	$79.27	12.820%	$89.4324	$89.43	$89.45	$89.40
7 purchase totals =	$604.96		$655.4467	$655.44	$655.45	$655.40