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	$62.62	4.253%	$65.2832	$65.28	$65.30	$65.30
Purchase #2	$99.65	3.852%	$103.4885	$103.49	$103.50	$103.50
Purchase #3	$134.95	6.685%	$143.9714	$143.97	$143.95	$144.00
Purchase #4	$94.80	9.459%	$103.7671	$103.77	$103.75	$103.80
Purchase #5	$41.60	12.315%	$46.723	$46.72	$46.70	$46.70
Purchase #6	$142.53	3.764%	$147.8948	$147.89	$147.90	$147.90
Purchase #7	$30.54	12.377%	$34.3199	$34.32	$34.30	$34.30
7 purchase totals =	$606.69		$645.4479	$645.44	$645.40	$645.50