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	$199.79	6.812%	$213.3997	$213.40	$213.40	$213.40
Purchase #2	$34.77	13.627%	$39.5081	$39.51	$39.50	$39.50
Purchase #3	$58.82	11.399%	$65.5249	$65.52	$65.50	$65.50
Purchase #4	$100.53	8.439%	$109.0137	$109.01	$109.00	$109.00
Purchase #5	$37.63	13.629%	$42.7586	$42.76	$42.75	$42.80
Purchase #6	$211.90	6.141%	$224.9128	$224.91	$224.90	$224.90
Purchase #7	$138.60	9.781%	$152.1565	$152.16	$152.15	$152.20
7 purchase totals =	$782.04		$847.2743	$847.27	$847.20	$847.30