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	$139.69	3.186%	$144.1405	$144.14	$144.15	$144.10
Purchase #2	$60.97	3.811%	$63.2936	$63.29	$63.30	$63.30
Purchase #3	$27.37	10.467%	$30.2348	$30.23	$30.25	$30.20
Purchase #4	$225.56	7.230%	$241.868	$241.87	$241.85	$241.90
Purchase #5	$82.33	9.381%	$90.0534	$90.05	$90.05	$90.10
Purchase #6	$100.52	7.506%	$108.065	$108.07	$108.05	$108.10
Purchase #7	$146.33	3.355%	$151.2394	$151.24	$151.25	$151.20
7 purchase totals =	$782.77		$828.8947	$828.89	$828.90	$828.90