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	$39.90	6.445%	$42.4716	$42.47	$42.45	$42.50
Purchase #2	$18.89	8.170%	$20.4333	$20.43	$20.45	$20.40
Purchase #3	$200.79	10.336%	$221.5437	$221.54	$221.55	$221.50
Purchase #4	$86.79	3.501%	$89.8285	$89.83	$89.85	$89.80
Purchase #5	$31.37	10.307%	$34.6033	$34.60	$34.60	$34.60
Purchase #6	$57.69	6.738%	$61.5772	$61.58	$61.60	$61.60
Purchase #7	$202.98	4.755%	$212.6317	$212.63	$212.65	$212.60
7 purchase totals =	$638.41		$683.0893	$683.08	$683.15	$683.00