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	$244.98	4.569%	$256.1731	$256.17	$256.15	$256.20
Purchase #2	$80.33	12.108%	$90.0564	$90.06	$90.05	$90.10
Purchase #3	$217.61	4.341%	$227.0565	$227.06	$227.05	$227.10
Purchase #4	$170.86	8.290%	$185.0243	$185.02	$185.00	$185.00
Purchase #5	$151.97	12.345%	$170.7307	$170.73	$170.75	$170.70
Purchase #6	$99.77	5.429%	$105.1865	$105.19	$105.20	$105.20
Purchase #7	$42.66	9.864%	$46.868	$46.87	$46.85	$46.90
7 purchase totals =	$1,008.18		$1,081.0955	$1,081.10	$1,081.05	$1,081.20