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	$52.72	11.663%	$58.8687	$58.87	$58.85	$58.90
Purchase #2	$77.96	5.626%	$82.346	$82.35	$82.35	$82.30
Purchase #3	$140.65	6.286%	$149.4913	$149.49	$149.50	$149.50
Purchase #4	$83.49	4.600%	$87.3305	$87.33	$87.35	$87.30
Purchase #5	$51.45	7.842%	$55.4847	$55.48	$55.50	$55.50
Purchase #6	$79.38	13.509%	$90.1034	$90.10	$90.10	$90.10
Purchase #7	$161.39	12.165%	$181.0231	$181.02	$181.00	$181.00
7 purchase totals =	$647.04		$704.6477	$704.64	$704.65	$704.60