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	$93.43	6.167%	$99.1918	$99.19	$99.20	$99.20
Purchase #2	$55.76	12.437%	$62.6949	$62.69	$62.70	$62.70
Purchase #3	$20.72	5.323%	$21.8229	$21.82	$21.80	$21.80
Purchase #4	$20.94	4.405%	$21.8624	$21.86	$21.85	$21.90
Purchase #5	$44.52	3.851%	$46.2345	$46.23	$46.25	$46.20
Purchase #6	$199.51	12.736%	$224.9196	$224.92	$224.90	$224.90
Purchase #7	$93.31	12.868%	$105.3171	$105.32	$105.30	$105.30
7 purchase totals =	$528.19		$582.0432	$582.03	$582.00	$582.00