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	$242.78	9.263%	$265.2687	$265.27	$265.25	$265.30
Purchase #2	$71.29	11.356%	$79.3857	$79.39	$79.40	$79.40
Purchase #3	$177.32	4.263%	$184.8792	$184.88	$184.90	$184.90
Purchase #4	$87.82	12.469%	$98.7703	$98.77	$98.75	$98.80
Purchase #5	$58.89	4.669%	$61.6396	$61.64	$61.65	$61.60
Purchase #6	$72.59	6.662%	$77.4259	$77.43	$77.45	$77.40
Purchase #7	$28.36	13.585%	$32.2127	$32.21	$32.20	$32.20
7 purchase totals =	$739.05		$799.5821	$799.59	$799.60	$799.60