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	$26.67	7.265%	$28.6076	$28.61	$28.60	$28.60
Purchase #2	$167.70	13.445%	$190.2473	$190.25	$190.25	$190.20
Purchase #3	$109.75	5.361%	$115.6337	$115.63	$115.65	$115.60
Purchase #4	$149.31	7.424%	$160.3948	$160.39	$160.40	$160.40
Purchase #5	$59.81	6.830%	$63.895	$63.90	$63.90	$63.90
Purchase #6	$186.32	7.575%	$200.4337	$200.43	$200.45	$200.40
Purchase #7	$97.50	3.151%	$100.5722	$100.57	$100.55	$100.60
7 purchase totals =	$797.06		$859.7843	$859.78	$859.80	$859.70