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	$36.46	7.669%	$39.2561	$39.26	$39.25	$39.30
Purchase #2	$12.33	10.601%	$13.6371	$13.64	$13.65	$13.60
Purchase #3	$187.52	13.215%	$212.3008	$212.30	$212.30	$212.30
Purchase #4	$48.60	12.387%	$54.6201	$54.62	$54.60	$54.60
Purchase #5	$115.89	13.804%	$131.8875	$131.89	$131.90	$131.90
Purchase #6	$16.33	8.259%	$17.6787	$17.68	$17.70	$17.70
Purchase #7	$146.77	12.718%	$165.4362	$165.44	$165.45	$165.40
7 purchase totals =	$563.90		$634.8165	$634.83	$634.85	$634.80