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	$75.40	7.234%	$80.8544	$80.85	$80.85	$80.90
Purchase #2	$121.72	4.767%	$127.5224	$127.52	$127.50	$127.50
Purchase #3	$10.72	9.369%	$11.7244	$11.72	$11.70	$11.70
Purchase #4	$242.71	3.642%	$251.5495	$251.55	$251.55	$251.50
Purchase #5	$115.84	6.852%	$123.7774	$123.78	$123.80	$123.80
Purchase #6	$243.80	6.450%	$259.5251	$259.53	$259.55	$259.50
Purchase #7	$99.52	7.372%	$106.8566	$106.86	$106.85	$106.90
7 purchase totals =	$909.71		$961.8098	$961.81	$961.80	$961.80