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	$221.94	3.372%	$229.4238	$229.42	$229.40	$229.40
Purchase #2	$154.41	13.118%	$174.6655	$174.67	$174.65	$174.70
Purchase #3	$156.72	7.670%	$168.7404	$168.74	$168.75	$168.70
Purchase #4	$51.81	5.866%	$54.8492	$54.85	$54.85	$54.80
Purchase #5	$159.64	12.424%	$179.4737	$179.47	$179.45	$179.50
Purchase #6	$135.80	6.340%	$144.4097	$144.41	$144.40	$144.40
Purchase #7	$223.50	5.160%	$235.0326	$235.03	$235.05	$235.00
7 purchase totals =	$1,103.82		$1,186.5949	$1,186.59	$1,186.55	$1,186.50