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	$68.45	12.671%	$77.1233	$77.12	$77.10	$77.10
Purchase #2	$83.72	7.228%	$89.7713	$89.77	$89.75	$89.80
Purchase #3	$26.78	4.747%	$28.0512	$28.05	$28.05	$28.10
Purchase #4	$243.78	7.525%	$262.1244	$262.12	$262.10	$262.10
Purchase #5	$6.25	13.242%	$7.0776	$7.08	$7.10	$7.10
Purchase #6	$175.46	5.578%	$185.2472	$185.25	$185.25	$185.20
Purchase #7	$52.55	12.848%	$59.3016	$59.30	$59.30	$59.30
7 purchase totals =	$656.99		$708.6966	$708.69	$708.65	$708.70