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	$115.50	11.194%	$128.4291	$128.43	$128.45	$128.40
Purchase #2	$234.87	11.758%	$262.486	$262.49	$262.50	$262.50
Purchase #3	$18.99	13.740%	$21.5992	$21.60	$21.60	$21.60
Purchase #4	$142.84	6.727%	$152.4488	$152.45	$152.45	$152.40
Purchase #5	$122.83	9.142%	$134.0591	$134.06	$134.05	$134.10
Purchase #6	$30.53	6.372%	$32.4754	$32.48	$32.50	$32.50
Purchase #7	$13.33	10.573%	$14.7394	$14.74	$14.75	$14.70
7 purchase totals =	$678.89		$746.2370	$746.25	$746.30	$746.20