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	$98.99	7.719%	$106.631	$106.63	$106.65	$106.60
Purchase #2	$165.47	11.429%	$184.3816	$184.38	$184.40	$184.40
Purchase #3	$56.89	5.191%	$59.8432	$59.84	$59.85	$59.80
Purchase #4	$224.57	13.182%	$254.1728	$254.17	$254.15	$254.20
Purchase #5	$205.89	6.329%	$218.9208	$218.92	$218.90	$218.90
Purchase #6	$143.55	13.106%	$162.3637	$162.36	$162.35	$162.40
Purchase #7	$31.33	9.133%	$34.1914	$34.19	$34.20	$34.20
7 purchase totals =	$926.69		$1,020.5045	$1,020.49	$1,020.50	$1,020.50