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	$50.29	6.346%	$53.4814	$53.48	$53.50	$53.50
Purchase #2	$35.33	11.540%	$39.4071	$39.41	$39.40	$39.40
Purchase #3	$34.81	12.720%	$39.2378	$39.24	$39.25	$39.20
Purchase #4	$85.81	5.146%	$90.2258	$90.23	$90.25	$90.20
Purchase #5	$119.38	4.820%	$125.1341	$125.13	$125.15	$125.10
Purchase #6	$227.74	6.165%	$241.7802	$241.78	$241.80	$241.80
Purchase #7	$210.41	6.852%	$224.8273	$224.83	$224.85	$224.80
7 purchase totals =	$763.77		$814.0937	$814.10	$814.20	$814.00