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	$46.63	6.652%	$49.7318	$49.73	$49.75	$49.70
Purchase #2	$145.52	3.664%	$150.8519	$150.85	$150.85	$150.90
Purchase #3	$105.50	6.848%	$112.7246	$112.72	$112.70	$112.70
Purchase #4	$52.78	12.346%	$59.2962	$59.30	$59.30	$59.30
Purchase #5	$82.82	13.327%	$93.8574	$93.86	$93.85	$93.90
Purchase #6	$98.55	13.169%	$111.528	$111.53	$111.55	$111.50
Purchase #7	$119.85	8.256%	$129.7448	$129.74	$129.75	$129.70
7 purchase totals =	$651.65		$707.7347	$707.73	$707.75	$707.70