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	$124.65	6.507%	$132.761	$132.76	$132.75	$132.80
Purchase #2	$124.33	10.560%	$137.4592	$137.46	$137.45	$137.50
Purchase #3	$79.58	4.125%	$82.8627	$82.86	$82.85	$82.90
Purchase #4	$130.81	12.586%	$147.2737	$147.27	$147.25	$147.30
Purchase #5	$34.42	8.163%	$37.2297	$37.23	$37.25	$37.20
Purchase #6	$213.40	10.248%	$235.2692	$235.27	$235.25	$235.30
Purchase #7	$115.89	10.137%	$127.6378	$127.64	$127.65	$127.60
7 purchase totals =	$823.08		$900.4933	$900.49	$900.45	$900.60