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	$113.53	13.241%	$128.5625	$128.56	$128.55	$128.60
Purchase #2	$206.81	6.248%	$219.7315	$219.73	$219.75	$219.70
Purchase #3	$39.61	10.745%	$43.8661	$43.87	$43.85	$43.90
Purchase #4	$201.44	13.339%	$228.3101	$228.31	$228.30	$228.30
Purchase #5	$111.52	3.621%	$115.5581	$115.56	$115.55	$115.60
Purchase #6	$35.30	5.158%	$37.1208	$37.12	$37.10	$37.10
Purchase #7	$201.56	12.760%	$227.2791	$227.28	$227.30	$227.30
7 purchase totals =	$909.77		$1,000.4282	$1,000.43	$1,000.40	$1,000.50