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	$250.98	10.539%	$277.4308	$277.43	$277.45	$277.40
Purchase #2	$76.81	5.537%	$81.063	$81.06	$81.05	$81.10
Purchase #3	$115.44	10.267%	$127.2922	$127.29	$127.30	$127.30
Purchase #4	$80.42	6.451%	$85.6079	$85.61	$85.60	$85.60
Purchase #5	$240.51	4.152%	$250.496	$250.50	$250.50	$250.50
Purchase #6	$221.37	10.802%	$245.2824	$245.28	$245.30	$245.30
Purchase #7	$180.82	10.664%	$200.1026	$200.10	$200.10	$200.10
7 purchase totals =	$1,166.35		$1,267.2749	$1,267.27	$1,267.30	$1,267.30