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	$54.73	10.411%	$60.4279	$60.43	$60.45	$60.40
Purchase #2	$188.74	12.273%	$211.9041	$211.90	$211.90	$211.90
Purchase #3	$59.74	7.509%	$64.2259	$64.23	$64.25	$64.20
Purchase #4	$61.77	9.479%	$67.6252	$67.63	$67.65	$67.60
Purchase #5	$92.48	13.602%	$105.0591	$105.06	$105.05	$105.10
Purchase #6	$79.69	11.643%	$88.9683	$88.97	$88.95	$89.00
Purchase #7	$190.80	3.135%	$196.7816	$196.78	$196.80	$196.80
7 purchase totals =	$727.95		$794.9921	$795.00	$795.05	$795.00