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	$134.93	8.591%	$146.5218	$146.52	$146.50	$146.50
Purchase #2	$39.89	6.715%	$42.5686	$42.57	$42.55	$42.60
Purchase #3	$94.61	5.478%	$99.7927	$99.79	$99.80	$99.80
Purchase #4	$198.91	4.814%	$208.4855	$208.49	$208.50	$208.50
Purchase #5	$155.94	11.183%	$173.3788	$173.38	$173.40	$173.40
Purchase #6	$67.38	8.232%	$72.9267	$72.93	$72.95	$72.90
Purchase #7	$56.64	9.793%	$62.1868	$62.19	$62.20	$62.20
7 purchase totals =	$748.30		$805.8609	$805.87	$805.90	$805.90