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	$79.33	12.700%	$89.4049	$89.40	$89.40	$89.40
Purchase #2	$135.44	11.337%	$150.7948	$150.79	$150.80	$150.80
Purchase #3	$73.59	4.410%	$76.8353	$76.84	$76.85	$76.80
Purchase #4	$114.46	8.199%	$123.8446	$123.84	$123.85	$123.80
Purchase #5	$99.35	6.207%	$105.5167	$105.52	$105.50	$105.50
Purchase #6	$121.85	8.835%	$132.6154	$132.62	$132.60	$132.60
Purchase #7	$172.87	9.575%	$189.4223	$189.42	$189.40	$189.40
7 purchase totals =	$796.89		$868.4340	$868.43	$868.40	$868.30