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	$87.56	13.463%	$99.3482	$99.35	$99.35	$99.30
Purchase #2	$52.90	8.710%	$57.5076	$57.51	$57.50	$57.50
Purchase #3	$109.96	5.819%	$116.3586	$116.36	$116.35	$116.40
Purchase #4	$32.95	10.222%	$36.3181	$36.32	$36.30	$36.30
Purchase #5	$161.34	11.756%	$180.3071	$180.31	$180.30	$180.30
Purchase #6	$223.76	3.194%	$230.9069	$230.91	$230.90	$230.90
Purchase #7	$200.31	4.392%	$209.1076	$209.11	$209.10	$209.10
7 purchase totals =	$868.78		$929.8541	$929.87	$929.80	$929.80