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	$73.99	10.573%	$81.813	$81.81	$81.80	$81.80
Purchase #2	$150.25	3.555%	$155.5914	$155.59	$155.60	$155.60
Purchase #3	$14.74	3.590%	$15.2692	$15.27	$15.25	$15.30
Purchase #4	$191.27	7.507%	$205.6286	$205.63	$205.65	$205.60
Purchase #5	$84.94	5.261%	$89.4087	$89.41	$89.40	$89.40
Purchase #6	$100.84	9.603%	$110.5237	$110.52	$110.50	$110.50
Purchase #7	$136.64	10.386%	$150.8314	$150.83	$150.85	$150.80
7 purchase totals =	$752.67		$809.0660	$809.06	$809.05	$809.00