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	$130.61	12.218%	$146.5679	$146.57	$146.55	$146.60
Purchase #2	$218.40	7.358%	$234.4699	$234.47	$234.45	$234.50
Purchase #3	$82.69	11.846%	$92.4855	$92.49	$92.50	$92.50
Purchase #4	$101.32	4.182%	$105.5572	$105.56	$105.55	$105.60
Purchase #5	$235.32	3.483%	$243.5162	$243.52	$243.50	$243.50
Purchase #6	$30.47	7.554%	$32.7717	$32.77	$32.75	$32.80
Purchase #7	$63.69	8.685%	$69.2215	$69.22	$69.20	$69.20
7 purchase totals =	$862.50		$924.5899	$924.60	$924.50	$924.70