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	$134.26	12.224%	$150.6719	$150.67	$150.65	$150.70
Purchase #2	$74.53	10.405%	$82.2848	$82.28	$82.30	$82.30
Purchase #3	$219.27	3.432%	$226.7953	$226.80	$226.80	$226.80
Purchase #4	$41.96	9.144%	$45.7968	$45.80	$45.80	$45.80
Purchase #5	$28.59	6.841%	$30.5458	$30.55	$30.55	$30.50
Purchase #6	$48.86	6.827%	$52.1957	$52.20	$52.20	$52.20
Purchase #7	$56.35	10.859%	$62.469	$62.47	$62.45	$62.50
7 purchase totals =	$603.82		$650.7593	$650.77	$650.75	$650.80