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	$56.87	4.293%	$59.3114	$59.31	$59.30	$59.30
Purchase #2	$171.30	11.450%	$190.9139	$190.91	$190.90	$190.90
Purchase #3	$61.54	9.435%	$67.3463	$67.35	$67.35	$67.30
Purchase #4	$151.52	4.272%	$157.9929	$157.99	$158.00	$158.00
Purchase #5	$103.79	7.285%	$111.3511	$111.35	$111.35	$111.40
Purchase #6	$135.82	13.572%	$154.2535	$154.25	$154.25	$154.30
Purchase #7	$164.27	7.482%	$176.5607	$176.56	$176.55	$176.60
7 purchase totals =	$845.11		$917.7298	$917.72	$917.70	$917.80