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	$9.93	3.800%	$10.3073	$10.31	$10.30	$10.30
Purchase #2	$224.45	11.265%	$249.7343	$249.73	$249.75	$249.70
Purchase #3	$215.72	6.210%	$229.1162	$229.12	$229.10	$229.10
Purchase #4	$198.67	9.850%	$218.239	$218.24	$218.25	$218.20
Purchase #5	$56.72	9.861%	$62.3132	$62.31	$62.30	$62.30
Purchase #6	$232.92	13.594%	$264.5831	$264.58	$264.60	$264.60
Purchase #7	$102.26	13.753%	$116.3238	$116.32	$116.30	$116.30
7 purchase totals =	$1,040.67		$1,150.6169	$1,150.61	$1,150.60	$1,150.50