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	$249.58	10.496%	$275.7759	$275.78	$275.80	$275.80
Purchase #2	$178.39	6.595%	$190.1548	$190.15	$190.15	$190.20
Purchase #3	$69.38	12.130%	$77.7958	$77.80	$77.80	$77.80
Purchase #4	$244.97	13.169%	$277.2301	$277.23	$277.25	$277.20
Purchase #5	$115.76	6.524%	$123.3122	$123.31	$123.30	$123.30
Purchase #6	$98.50	5.539%	$103.9559	$103.96	$103.95	$104.00
Purchase #7	$105.80	12.616%	$119.1477	$119.15	$119.15	$119.10
7 purchase totals =	$1,062.38		$1,167.3724	$1,167.38	$1,167.40	$1,167.40