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	$171.80	4.476%	$179.4898	$179.49	$179.50	$179.50
Purchase #2	$51.53	9.720%	$56.5387	$56.54	$56.55	$56.50
Purchase #3	$46.77	10.872%	$51.8548	$51.85	$51.85	$51.90
Purchase #4	$72.70	12.331%	$81.6646	$81.66	$81.65	$81.70
Purchase #5	$103.87	5.232%	$109.3045	$109.30	$109.30	$109.30
Purchase #6	$125.28	13.674%	$142.4108	$142.41	$142.40	$142.40
Purchase #7	$60.59	6.620%	$64.6011	$64.60	$64.60	$64.60
7 purchase totals =	$632.54		$685.8643	$685.85	$685.85	$685.90