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	$74.88	3.595%	$77.5719	$77.57	$77.55	$77.60
Purchase #2	$141.33	10.676%	$156.4184	$156.42	$156.40	$156.40
Purchase #3	$64.51	6.279%	$68.5606	$68.56	$68.55	$68.60
Purchase #4	$100.95	3.614%	$104.5983	$104.60	$104.60	$104.60
Purchase #5	$149.82	5.530%	$158.105	$158.11	$158.10	$158.10
Purchase #6	$191.52	12.352%	$215.1766	$215.18	$215.20	$215.20
Purchase #7	$85.30	5.580%	$90.0597	$90.06	$90.05	$90.10
7 purchase totals =	$808.31		$870.4905	$870.50	$870.45	$870.60