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	$28.86	11.150%	$32.0779	$32.08	$32.10	$32.10
Purchase #2	$232.57	5.724%	$245.8823	$245.88	$245.90	$245.90
Purchase #3	$156.72	5.233%	$164.9212	$164.92	$164.90	$164.90
Purchase #4	$97.99	8.816%	$106.6288	$106.63	$106.65	$106.60
Purchase #5	$115.87	13.203%	$131.1683	$131.17	$131.15	$131.20
Purchase #6	$11.59	12.654%	$13.0566	$13.06	$13.05	$13.10
Purchase #7	$89.44	12.700%	$100.7989	$100.80	$100.80	$100.80
7 purchase totals =	$733.04		$794.5340	$794.54	$794.55	$794.60