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	$159.97	3.641%	$165.7945	$165.79	$165.80	$165.80
Purchase #2	$122.53	9.133%	$133.7207	$133.72	$133.70	$133.70
Purchase #3	$173.35	10.591%	$191.7095	$191.71	$191.70	$191.70
Purchase #4	$97.51	12.660%	$109.8548	$109.85	$109.85	$109.90
Purchase #5	$209.33	6.468%	$222.8695	$222.87	$222.85	$222.90
Purchase #6	$34.47	4.613%	$36.0601	$36.06	$36.05	$36.10
Purchase #7	$119.93	6.280%	$127.4616	$127.46	$127.45	$127.50
7 purchase totals =	$917.09		$987.4707	$987.46	$987.40	$987.60