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	$79.28	12.377%	$89.0925	$89.09	$89.10	$89.10
Purchase #2	$48.98	11.229%	$54.48	$54.48	$54.50	$54.50
Purchase #3	$103.59	4.453%	$108.2029	$108.20	$108.20	$108.20
Purchase #4	$187.64	11.567%	$209.3443	$209.34	$209.35	$209.30
Purchase #5	$94.58	4.736%	$99.0593	$99.06	$99.05	$99.10
Purchase #6	$12.60	8.340%	$13.6508	$13.65	$13.65	$13.70
Purchase #7	$64.44	5.234%	$67.8128	$67.81	$67.80	$67.80
7 purchase totals =	$591.11		$641.6426	$641.63	$641.65	$641.70