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	$19.29	10.627%	$21.3399	$21.34	$21.35	$21.30
Purchase #2	$200.83	3.575%	$208.0097	$208.01	$208.00	$208.00
Purchase #3	$111.76	10.670%	$123.6848	$123.68	$123.70	$123.70
Purchase #4	$132.31	7.400%	$142.1009	$142.10	$142.10	$142.10
Purchase #5	$152.33	6.841%	$162.7509	$162.75	$162.75	$162.80
Purchase #6	$250.94	4.189%	$261.4519	$261.45	$261.45	$261.50
Purchase #7	$159.48	7.758%	$171.8525	$171.85	$171.85	$171.90
7 purchase totals =	$1,026.94		$1,091.1906	$1,091.18	$1,091.20	$1,091.30