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	$5.26	5.165%	$5.5317	$5.53	$5.55	$5.50
Purchase #2	$74.83	10.594%	$82.7575	$82.76	$82.75	$82.80
Purchase #3	$222.44	5.591%	$234.8766	$234.88	$234.90	$234.90
Purchase #4	$115.31	4.596%	$120.6096	$120.61	$120.60	$120.60
Purchase #5	$160.96	7.662%	$173.2928	$173.29	$173.30	$173.30
Purchase #6	$36.59	3.646%	$37.9241	$37.92	$37.90	$37.90
Purchase #7	$22.74	12.263%	$25.5286	$25.53	$25.55	$25.50
7 purchase totals =	$638.13		$680.5209	$680.52	$680.55	$680.50