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	$230.62	8.455%	$250.1189	$250.12	$250.10	$250.10
Purchase #2	$50.58	6.532%	$53.8839	$53.88	$53.90	$53.90
Purchase #3	$63.95	8.347%	$69.2879	$69.29	$69.30	$69.30
Purchase #4	$106.38	9.282%	$116.2542	$116.25	$116.25	$116.30
Purchase #5	$38.93	11.827%	$43.5343	$43.53	$43.55	$43.50
Purchase #6	$112.56	13.132%	$127.3414	$127.34	$127.35	$127.30
Purchase #7	$245.33	4.142%	$255.4916	$255.49	$255.50	$255.50
7 purchase totals =	$848.35		$915.9122	$915.90	$915.95	$915.90