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	$79.41	13.357%	$90.0168	$90.02	$90.00	$90.00
Purchase #2	$154.55	7.739%	$166.5106	$166.51	$166.50	$166.50
Purchase #3	$194.54	7.275%	$208.6928	$208.69	$208.70	$208.70
Purchase #4	$64.43	9.155%	$70.3286	$70.33	$70.35	$70.30
Purchase #5	$56.90	5.546%	$60.0557	$60.06	$60.05	$60.10
Purchase #6	$167.52	6.507%	$178.4205	$178.42	$178.40	$178.40
Purchase #7	$179.65	6.629%	$191.559	$191.56	$191.55	$191.60
7 purchase totals =	$897.00		$965.5840	$965.59	$965.55	$965.60