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	$249.69	10.194%	$275.1434	$275.14	$275.15	$275.10
Purchase #2	$235.54	7.431%	$253.043	$253.04	$253.05	$253.00
Purchase #3	$129.37	4.346%	$134.9924	$134.99	$135.00	$135.00
Purchase #4	$114.30	8.367%	$123.8635	$123.86	$123.85	$123.90
Purchase #5	$53.73	10.307%	$59.268	$59.27	$59.25	$59.30
Purchase #6	$141.43	13.136%	$160.0082	$160.01	$160.00	$160.00
Purchase #7	$113.39	10.633%	$125.4468	$125.45	$125.45	$125.40
7 purchase totals =	$1,037.45		$1,131.7653	$1,131.76	$1,131.75	$1,131.70