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	$216.94	5.660%	$229.2188	$229.22	$229.20	$229.20
Purchase #2	$137.77	3.253%	$142.2517	$142.25	$142.25	$142.30
Purchase #3	$166.75	5.106%	$175.2643	$175.26	$175.25	$175.30
Purchase #4	$115.44	10.257%	$127.2807	$127.28	$127.30	$127.30
Purchase #5	$36.85	7.362%	$39.5629	$39.56	$39.55	$39.60
Purchase #6	$35.44	9.395%	$38.7696	$38.77	$38.75	$38.80
Purchase #7	$74.93	11.495%	$83.5432	$83.54	$83.55	$83.50
7 purchase totals =	$784.12		$835.8912	$835.88	$835.85	$836.00