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	$14.83	3.235%	$15.3098	$15.31	$15.30	$15.30
Purchase #2	$109.94	13.850%	$125.1667	$125.17	$125.15	$125.20
Purchase #3	$109.61	9.860%	$120.4175	$120.42	$120.40	$120.40
Purchase #4	$170.77	8.456%	$185.2103	$185.21	$185.20	$185.20
Purchase #5	$83.53	8.167%	$90.3519	$90.35	$90.35	$90.40
Purchase #6	$239.94	5.406%	$252.9112	$252.91	$252.90	$252.90
Purchase #7	$79.55	12.308%	$89.341	$89.34	$89.35	$89.30
7 purchase totals =	$808.17		$878.7084	$878.71	$878.65	$878.70