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	$14.62	8.839%	$15.9123	$15.91	$15.90	$15.90
Purchase #2	$41.59	10.720%	$46.0484	$46.05	$46.05	$46.00
Purchase #3	$171.82	11.370%	$191.3559	$191.36	$191.35	$191.40
Purchase #4	$180.77	8.531%	$196.1915	$196.19	$196.20	$196.20
Purchase #5	$50.75	7.113%	$54.3598	$54.36	$54.35	$54.40
Purchase #6	$174.40	12.538%	$196.2663	$196.27	$196.25	$196.30
Purchase #7	$75.69	13.514%	$85.9187	$85.92	$85.90	$85.90
7 purchase totals =	$709.64		$786.0529	$786.06	$786.00	$786.10