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	$16.73	12.508%	$18.8226	$18.82	$18.80	$18.80
Purchase #2	$184.69	3.296%	$190.7774	$190.78	$190.80	$190.80
Purchase #3	$102.98	8.112%	$111.3337	$111.33	$111.35	$111.30
Purchase #4	$95.38	13.573%	$108.3259	$108.33	$108.35	$108.30
Purchase #5	$95.36	10.244%	$105.1287	$105.13	$105.15	$105.10
Purchase #6	$149.94	12.227%	$168.2732	$168.27	$168.25	$168.30
Purchase #7	$60.72	6.657%	$64.7621	$64.76	$64.75	$64.80
7 purchase totals =	$705.80		$767.4236	$767.42	$767.45	$767.40