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	$228.78	6.399%	$243.4196	$243.42	$243.40	$243.40
Purchase #2	$221.75	13.155%	$250.9212	$250.92	$250.90	$250.90
Purchase #3	$57.70	9.679%	$63.2848	$63.28	$63.30	$63.30
Purchase #4	$217.71	5.569%	$229.8343	$229.83	$229.85	$229.80
Purchase #5	$199.27	10.828%	$220.847	$220.85	$220.85	$220.80
Purchase #6	$111.43	12.139%	$124.9565	$124.96	$124.95	$125.00
Purchase #7	$156.90	5.562%	$165.6268	$165.63	$165.65	$165.60
7 purchase totals =	$1,193.54		$1,298.8902	$1,298.89	$1,298.90	$1,298.80