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	$90.98	10.802%	$100.8077	$100.81	$100.80	$100.80
Purchase #2	$238.69	12.434%	$268.3687	$268.37	$268.35	$268.40
Purchase #3	$181.95	6.765%	$194.2589	$194.26	$194.25	$194.30
Purchase #4	$150.76	5.753%	$159.4332	$159.43	$159.45	$159.40
Purchase #5	$140.38	6.421%	$149.3938	$149.39	$149.40	$149.40
Purchase #6	$37.50	12.448%	$42.168	$42.17	$42.15	$42.20
Purchase #7	$93.38	7.714%	$100.5833	$100.58	$100.60	$100.60
7 purchase totals =	$933.64		$1,015.0136	$1,015.01	$1,015.00	$1,015.10