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	$101.28	8.551%	$109.9405	$109.94	$109.95	$109.90
Purchase #2	$205.75	12.446%	$231.3576	$231.36	$231.35	$231.40
Purchase #3	$226.61	3.650%	$234.8813	$234.88	$234.90	$234.90
Purchase #4	$98.94	7.405%	$106.2665	$106.27	$106.25	$106.30
Purchase #5	$48.66	11.147%	$54.0841	$54.08	$54.10	$54.10
Purchase #6	$105.91	5.150%	$111.3644	$111.36	$111.35	$111.40
Purchase #7	$36.63	13.302%	$41.5025	$41.50	$41.50	$41.50
7 purchase totals =	$823.78		$889.3969	$889.39	$889.40	$889.50