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	$79.51	12.851%	$89.7278	$89.73	$89.75	$89.70
Purchase #2	$90.27	10.854%	$100.0679	$100.07	$100.05	$100.10
Purchase #3	$89.72	3.474%	$92.8369	$92.84	$92.85	$92.80
Purchase #4	$40.97	11.291%	$45.5959	$45.60	$45.60	$45.60
Purchase #5	$63.91	10.373%	$70.5394	$70.54	$70.55	$70.50
Purchase #6	$68.89	10.367%	$76.0318	$76.03	$76.05	$76.00
Purchase #7	$174.64	9.443%	$191.1313	$191.13	$191.15	$191.10
7 purchase totals =	$607.91		$665.9310	$665.94	$666.00	$665.80