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	$26.92	11.208%	$29.9372	$29.94	$29.95	$29.90
Purchase #2	$76.78	10.772%	$85.0507	$85.05	$85.05	$85.10
Purchase #3	$191.26	4.648%	$200.1498	$200.15	$200.15	$200.10
Purchase #4	$93.28	13.149%	$105.5454	$105.55	$105.55	$105.50
Purchase #5	$72.86	3.533%	$75.4341	$75.43	$75.45	$75.40
Purchase #6	$156.62	5.642%	$165.4565	$165.46	$165.45	$165.50
Purchase #7	$52.34	6.823%	$55.9112	$55.91	$55.90	$55.90
7 purchase totals =	$670.06		$717.4849	$717.49	$717.50	$717.40