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	$160.65	6.156%	$170.5396	$170.54	$170.55	$170.50
Purchase #2	$236.28	9.457%	$258.625	$258.63	$258.65	$258.60
Purchase #3	$207.95	6.534%	$221.5375	$221.54	$221.55	$221.50
Purchase #4	$173.76	13.137%	$196.5869	$196.59	$196.60	$196.60
Purchase #5	$89.73	10.311%	$98.9821	$98.98	$99.00	$99.00
Purchase #6	$235.45	11.684%	$262.96	$262.96	$262.95	$263.00
Purchase #7	$158.39	11.505%	$176.6128	$176.61	$176.60	$176.60
7 purchase totals =	$1,262.21		$1,385.8439	$1,385.85	$1,385.90	$1,385.80