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	$83.59	7.744%	$90.0632	$90.06	$90.05	$90.10
Purchase #2	$9.89	3.773%	$10.2631	$10.26	$10.25	$10.30
Purchase #3	$166.31	9.200%	$181.6105	$181.61	$181.60	$181.60
Purchase #4	$91.92	13.220%	$104.0718	$104.07	$104.05	$104.10
Purchase #5	$122.34	4.795%	$128.2062	$128.21	$128.20	$128.20
Purchase #6	$169.66	5.791%	$179.485	$179.49	$179.50	$179.50
Purchase #7	$144.46	5.286%	$152.0962	$152.10	$152.10	$152.10
7 purchase totals =	$788.17		$845.7960	$845.80	$845.75	$845.90