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	$156.52	5.161%	$164.598	$164.60	$164.60	$164.60
Purchase #2	$198.63	13.413%	$225.2722	$225.27	$225.25	$225.30
Purchase #3	$33.95	10.529%	$37.5246	$37.52	$37.50	$37.50
Purchase #4	$181.37	4.765%	$190.0123	$190.01	$190.00	$190.00
Purchase #5	$13.33	8.621%	$14.4792	$14.48	$14.50	$14.50
Purchase #6	$244.76	12.557%	$275.4945	$275.49	$275.50	$275.50
Purchase #7	$33.84	12.459%	$38.0561	$38.06	$38.05	$38.10
7 purchase totals =	$862.40		$945.4369	$945.43	$945.40	$945.50