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	$40.54	11.460%	$45.1859	$45.19	$45.20	$45.20
Purchase #2	$208.88	10.334%	$230.4657	$230.47	$230.45	$230.50
Purchase #3	$180.46	10.729%	$199.8216	$199.82	$199.80	$199.80
Purchase #4	$137.85	4.277%	$143.7458	$143.75	$143.75	$143.70
Purchase #5	$168.46	13.371%	$190.9848	$190.98	$191.00	$191.00
Purchase #6	$63.31	11.794%	$70.7768	$70.78	$70.80	$70.80
Purchase #7	$62.59	8.212%	$67.7299	$67.73	$67.75	$67.70
7 purchase totals =	$862.09		$948.7105	$948.72	$948.75	$948.70