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	$20.54	9.211%	$22.4319	$22.43	$22.45	$22.40
Purchase #2	$124.40	9.691%	$136.4556	$136.46	$136.45	$136.50
Purchase #3	$238.37	13.453%	$270.4379	$270.44	$270.45	$270.40
Purchase #4	$99.49	4.176%	$103.6447	$103.64	$103.65	$103.60
Purchase #5	$83.31	7.175%	$89.2875	$89.29	$89.30	$89.30
Purchase #6	$215.94	12.420%	$242.7597	$242.76	$242.75	$242.80
Purchase #7	$71.39	9.479%	$78.1571	$78.16	$78.15	$78.20
7 purchase totals =	$853.44		$943.1744	$943.18	$943.20	$943.20