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	$109.81	7.811%	$118.3873	$118.39	$118.40	$118.40
Purchase #2	$228.87	10.684%	$253.3225	$253.32	$253.30	$253.30
Purchase #3	$99.31	10.302%	$109.5409	$109.54	$109.55	$109.50
Purchase #4	$146.53	10.418%	$161.7955	$161.80	$161.80	$161.80
Purchase #5	$194.56	4.362%	$203.0467	$203.05	$203.05	$203.00
Purchase #6	$137.84	5.476%	$145.3881	$145.39	$145.40	$145.40
Purchase #7	$100.25	9.606%	$109.88	$109.88	$109.90	$109.90
7 purchase totals =	$1,017.17		$1,101.3610	$1,101.37	$1,101.40	$1,101.30