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	$6.87	4.119%	$7.153	$7.15	$7.15	$7.20
Purchase #2	$146.75	3.829%	$152.3691	$152.37	$152.35	$152.40
Purchase #3	$137.41	8.812%	$149.5186	$149.52	$149.50	$149.50
Purchase #4	$19.58	3.390%	$20.2438	$20.24	$20.25	$20.20
Purchase #5	$13.69	3.418%	$14.1579	$14.16	$14.15	$14.20
Purchase #6	$78.72	4.301%	$82.1057	$82.11	$82.10	$82.10
Purchase #7	$62.58	12.487%	$70.3944	$70.39	$70.40	$70.40
7 purchase totals =	$465.60		$495.9425	$495.94	$495.90	$496.00