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	$115.33	10.309%	$127.2194	$127.22	$127.20	$127.20
Purchase #2	$165.79	8.715%	$180.2386	$180.24	$180.25	$180.20
Purchase #3	$141.54	12.751%	$159.5878	$159.59	$159.60	$159.60
Purchase #4	$36.57	8.301%	$39.6057	$39.61	$39.60	$39.60
Purchase #5	$236.85	5.666%	$250.2699	$250.27	$250.25	$250.30
Purchase #6	$98.66	12.517%	$111.0093	$111.01	$111.00	$111.00
Purchase #7	$205.52	12.221%	$230.6366	$230.64	$230.65	$230.60
7 purchase totals =	$1,000.26		$1,098.5673	$1,098.58	$1,098.55	$1,098.50