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	$16.91	9.808%	$18.5685	$18.57	$18.55	$18.60
Purchase #2	$55.84	5.847%	$59.105	$59.11	$59.10	$59.10
Purchase #3	$220.89	8.322%	$239.2725	$239.27	$239.25	$239.30
Purchase #4	$150.46	5.304%	$158.4404	$158.44	$158.45	$158.40
Purchase #5	$227.34	6.500%	$242.1171	$242.12	$242.10	$242.10
Purchase #6	$123.55	3.690%	$128.109	$128.11	$128.10	$128.10
Purchase #7	$154.48	4.497%	$161.427	$161.43	$161.45	$161.40
7 purchase totals =	$949.47		$1,007.0395	$1,007.05	$1,007.00	$1,007.00