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	$26.77	6.423%	$28.4894	$28.49	$28.50	$28.50
Purchase #2	$99.75	5.813%	$105.5485	$105.55	$105.55	$105.50
Purchase #3	$53.87	5.592%	$56.8824	$56.88	$56.90	$56.90
Purchase #4	$164.27	9.438%	$179.7738	$179.77	$179.75	$179.80
Purchase #5	$250.26	3.786%	$259.7348	$259.73	$259.75	$259.70
Purchase #6	$150.80	5.362%	$158.8859	$158.89	$158.90	$158.90
Purchase #7	$83.26	10.670%	$92.1438	$92.14	$92.15	$92.10
7 purchase totals =	$828.98		$881.4586	$881.45	$881.50	$881.40