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	$60.64	5.401%	$63.9152	$63.92	$63.90	$63.90
Purchase #2	$179.56	5.777%	$189.9332	$189.93	$189.95	$189.90
Purchase #3	$150.53	11.280%	$167.5098	$167.51	$167.50	$167.50
Purchase #4	$6.99	6.565%	$7.4489	$7.45	$7.45	$7.40
Purchase #5	$103.59	9.600%	$113.5346	$113.53	$113.55	$113.50
Purchase #6	$18.65	3.804%	$19.3594	$19.36	$19.35	$19.40
Purchase #7	$57.69	6.171%	$61.25	$61.25	$61.25	$61.30
7 purchase totals =	$577.65		$622.9511	$622.95	$622.95	$622.90