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	$225.49	7.551%	$242.5167	$242.52	$242.50	$242.50
Purchase #2	$49.69	10.325%	$54.8205	$54.82	$54.80	$54.80
Purchase #3	$170.56	8.478%	$185.0201	$185.02	$185.00	$185.00
Purchase #4	$203.87	9.547%	$223.3335	$223.33	$223.35	$223.30
Purchase #5	$218.59	7.356%	$234.6695	$234.67	$234.65	$234.70
Purchase #6	$98.60	5.330%	$103.8554	$103.86	$103.85	$103.90
Purchase #7	$150.82	11.106%	$167.5701	$167.57	$167.55	$167.60
7 purchase totals =	$1,117.62		$1,211.7858	$1,211.79	$1,211.70	$1,211.80