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	$205.68	13.418%	$233.2781	$233.28	$233.30	$233.30
Purchase #2	$147.44	3.646%	$152.8157	$152.82	$152.80	$152.80
Purchase #3	$36.95	11.670%	$41.2621	$41.26	$41.25	$41.30
Purchase #4	$175.71	5.610%	$185.5673	$185.57	$185.55	$185.60
Purchase #5	$105.82	13.863%	$120.4898	$120.49	$120.50	$120.50
Purchase #6	$49.90	11.453%	$55.615	$55.62	$55.60	$55.60
Purchase #7	$61.72	9.858%	$67.8044	$67.80	$67.80	$67.80
7 purchase totals =	$783.22		$856.8324	$856.84	$856.80	$856.90