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	$50.60	7.728%	$54.5104	$54.51	$54.50	$54.50
Purchase #2	$240.26	5.576%	$253.6569	$253.66	$253.65	$253.70
Purchase #3	$232.87	9.429%	$254.8273	$254.83	$254.85	$254.80
Purchase #4	$169.53	12.825%	$191.2722	$191.27	$191.25	$191.30
Purchase #5	$245.96	3.259%	$253.9758	$253.98	$254.00	$254.00
Purchase #6	$103.61	6.488%	$110.3322	$110.33	$110.35	$110.30
Purchase #7	$185.72	5.779%	$196.4528	$196.45	$196.45	$196.50
7 purchase totals =	$1,228.55		$1,315.0276	$1,315.03	$1,315.05	$1,315.10