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	$42.27	10.649%	$46.7713	$46.77	$46.75	$46.80
Purchase #2	$189.76	5.695%	$200.5668	$200.57	$200.55	$200.60
Purchase #3	$208.71	7.147%	$223.6265	$223.63	$223.65	$223.60
Purchase #4	$115.40	11.690%	$128.8903	$128.89	$128.90	$128.90
Purchase #5	$43.28	4.827%	$45.3691	$45.37	$45.35	$45.40
Purchase #6	$52.75	6.525%	$56.1919	$56.19	$56.20	$56.20
Purchase #7	$165.93	5.834%	$175.6104	$175.61	$175.60	$175.60
7 purchase totals =	$818.10		$877.0263	$877.03	$877.00	$877.10