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	$86.78	8.498%	$94.1546	$94.15	$94.15	$94.20
Purchase #2	$32.65	11.624%	$36.4452	$36.45	$36.45	$36.40
Purchase #3	$116.65	12.193%	$130.8731	$130.87	$130.85	$130.90
Purchase #4	$70.40	11.608%	$78.572	$78.57	$78.55	$78.60
Purchase #5	$39.49	7.759%	$42.554	$42.55	$42.55	$42.60
Purchase #6	$98.39	8.415%	$106.6695	$106.67	$106.65	$106.70
Purchase #7	$137.38	11.729%	$153.4933	$153.49	$153.50	$153.50
7 purchase totals =	$581.74		$642.7617	$642.75	$642.70	$642.90