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	9.698%	$57.8328	$57.83	$57.85	$57.80
Purchase #2	$171.53	5.345%	$180.6983	$180.70	$180.70	$180.70
Purchase #3	$64.81	9.251%	$70.8056	$70.81	$70.80	$70.80
Purchase #4	$144.78	10.427%	$159.8762	$159.88	$159.90	$159.90
Purchase #5	$93.45	6.846%	$99.8476	$99.85	$99.85	$99.80
Purchase #6	$137.94	12.357%	$154.9852	$154.99	$155.00	$155.00
Purchase #7	$85.92	7.623%	$92.4697	$92.47	$92.45	$92.50
7 purchase totals =	$751.15		$816.5154	$816.53	$816.55	$816.50