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	$72.89	11.232%	$81.077	$81.08	$81.10	$81.10
Purchase #2	$144.32	4.656%	$151.0395	$151.04	$151.05	$151.00
Purchase #3	$69.61	3.775%	$72.2378	$72.24	$72.25	$72.20
Purchase #4	$241.79	13.346%	$274.0593	$274.06	$274.05	$274.10
Purchase #5	$21.42	6.566%	$22.8264	$22.83	$22.85	$22.80
Purchase #6	$134.85	11.658%	$150.5708	$150.57	$150.55	$150.60
Purchase #7	$172.79	10.642%	$191.1783	$191.18	$191.20	$191.20
7 purchase totals =	$857.67		$942.9891	$943.00	$943.05	$943.00