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	$103.45	3.102%	$106.659	$106.66	$106.65	$106.70
Purchase #2	$143.85	4.726%	$150.6484	$150.65	$150.65	$150.60
Purchase #3	$202.53	9.179%	$221.1202	$221.12	$221.10	$221.10
Purchase #4	$95.64	9.472%	$104.699	$104.70	$104.70	$104.70
Purchase #5	$32.76	13.129%	$37.0611	$37.06	$37.05	$37.10
Purchase #6	$104.75	4.196%	$109.1453	$109.15	$109.15	$109.10
Purchase #7	$104.34	5.281%	$109.8502	$109.85	$109.85	$109.90
7 purchase totals =	$787.32		$839.1832	$839.19	$839.15	$839.20