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	$127.41	4.649%	$133.3333	$133.33	$133.35	$133.30
Purchase #2	$133.60	3.237%	$137.9246	$137.92	$137.90	$137.90
Purchase #3	$162.91	4.721%	$170.601	$170.60	$170.60	$170.60
Purchase #4	$80.25	7.144%	$85.9831	$85.98	$86.00	$86.00
Purchase #5	$101.67	4.138%	$105.8771	$105.88	$105.90	$105.90
Purchase #6	$65.91	6.412%	$70.1361	$70.14	$70.15	$70.10
Purchase #7	$131.52	5.809%	$139.16	$139.16	$139.15	$139.20
7 purchase totals =	$803.27		$843.0152	$843.01	$843.05	$843.00