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	$37.84	12.667%	$42.6332	$42.63	$42.65	$42.60
Purchase #2	$68.34	3.671%	$70.8488	$70.85	$70.85	$70.80
Purchase #3	$191.55	9.265%	$209.2971	$209.30	$209.30	$209.30
Purchase #4	$141.35	3.629%	$146.4796	$146.48	$146.50	$146.50
Purchase #5	$247.55	3.115%	$255.2612	$255.26	$255.25	$255.30
Purchase #6	$53.81	9.869%	$59.1205	$59.12	$59.10	$59.10
Purchase #7	$71.80	11.500%	$80.057	$80.06	$80.05	$80.10
7 purchase totals =	$812.24		$863.6974	$863.70	$863.70	$863.70