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	$18.81	13.524%	$21.3539	$21.35	$21.35	$21.40
Purchase #2	$249.71	10.870%	$276.8535	$276.85	$276.85	$276.90
Purchase #3	$136.30	6.716%	$145.4539	$145.45	$145.45	$145.50
Purchase #4	$189.43	3.250%	$195.5865	$195.59	$195.60	$195.60
Purchase #5	$41.83	7.688%	$45.0459	$45.05	$45.05	$45.00
Purchase #6	$173.92	10.192%	$191.6459	$191.65	$191.65	$191.60
Purchase #7	$169.69	10.251%	$187.0849	$187.08	$187.10	$187.10
7 purchase totals =	$979.69		$1,063.0245	$1,063.02	$1,063.05	$1,063.10