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	$108.87	5.129%	$114.4539	$114.45	$114.45	$114.50
Purchase #2	$169.27	7.364%	$181.735	$181.74	$181.75	$181.70
Purchase #3	$18.76	11.352%	$20.8896	$20.89	$20.90	$20.90
Purchase #4	$151.25	6.826%	$161.5743	$161.57	$161.55	$161.60
Purchase #5	$34.25	9.333%	$37.4466	$37.45	$37.45	$37.40
Purchase #6	$213.48	13.388%	$242.0607	$242.06	$242.05	$242.10
Purchase #7	$211.49	13.658%	$240.3753	$240.38	$240.40	$240.40
7 purchase totals =	$907.37		$998.5354	$998.54	$998.55	$998.60