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	$189.66	3.721%	$196.7172	$196.72	$196.70	$196.70
Purchase #2	$126.87	12.333%	$142.5169	$142.52	$142.50	$142.50
Purchase #3	$59.66	8.428%	$64.6881	$64.69	$64.70	$64.70
Purchase #4	$71.73	13.118%	$81.1395	$81.14	$81.15	$81.10
Purchase #5	$63.73	9.190%	$69.5868	$69.59	$69.60	$69.60
Purchase #6	$18.43	8.345%	$19.968	$19.97	$19.95	$20.00
Purchase #7	$127.87	7.320%	$137.2301	$137.23	$137.25	$137.20
7 purchase totals =	$657.95		$711.8466	$711.86	$711.85	$711.80