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	$38.83	9.491%	$42.5154	$42.52	$42.50	$42.50
Purchase #2	$115.49	3.458%	$119.4836	$119.48	$119.50	$119.50
Purchase #3	$178.42	5.774%	$188.722	$188.72	$188.70	$188.70
Purchase #4	$89.76	11.825%	$100.3741	$100.37	$100.35	$100.40
Purchase #5	$239.27	6.261%	$254.2507	$254.25	$254.25	$254.30
Purchase #6	$106.72	3.305%	$110.2471	$110.25	$110.25	$110.20
Purchase #7	$72.27	9.341%	$79.0207	$79.02	$79.00	$79.00
7 purchase totals =	$840.76		$894.6136	$894.61	$894.55	$894.60