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	$172.27	4.421%	$179.8861	$179.89	$179.90	$179.90
Purchase #2	$30.69	8.404%	$33.2692	$33.27	$33.25	$33.30
Purchase #3	$53.80	3.395%	$55.6265	$55.63	$55.65	$55.60
Purchase #4	$73.35	7.600%	$78.9246	$78.92	$78.90	$78.90
Purchase #5	$146.69	12.367%	$164.8312	$164.83	$164.85	$164.80
Purchase #6	$95.31	9.616%	$104.475	$104.48	$104.50	$104.50
Purchase #7	$246.32	13.491%	$279.551	$279.55	$279.55	$279.60
7 purchase totals =	$818.43		$896.5636	$896.57	$896.60	$896.60