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	$20.85	4.255%	$21.7372	$21.74	$21.75	$21.70
Purchase #2	$79.89	3.131%	$82.3914	$82.39	$82.40	$82.40
Purchase #3	$98.73	4.377%	$103.0514	$103.05	$103.05	$103.10
Purchase #4	$197.97	13.643%	$224.979	$224.98	$225.00	$225.00
Purchase #5	$90.59	10.285%	$99.9072	$99.91	$99.90	$99.90
Purchase #6	$122.37	6.523%	$130.3522	$130.35	$130.35	$130.40
Purchase #7	$183.65	11.274%	$204.3547	$204.35	$204.35	$204.40
7 purchase totals =	$794.05		$866.7731	$866.77	$866.80	$866.90