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	$116.78	6.169%	$123.9842	$123.98	$124.00	$124.00
Purchase #2	$62.83	4.685%	$65.7736	$65.77	$65.75	$65.80
Purchase #3	$48.49	5.860%	$51.3315	$51.33	$51.35	$51.30
Purchase #4	$159.62	5.528%	$168.4438	$168.44	$168.45	$168.40
Purchase #5	$23.84	4.114%	$24.8208	$24.82	$24.80	$24.80
Purchase #6	$228.87	5.114%	$240.5744	$240.57	$240.55	$240.60
Purchase #7	$150.46	6.132%	$159.6862	$159.69	$159.70	$159.70
7 purchase totals =	$790.89		$834.6145	$834.60	$834.60	$834.60