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	$231.50	8.483%	$251.1381	$251.14	$251.15	$251.10
Purchase #2	$146.72	12.820%	$165.5295	$165.53	$165.55	$165.50
Purchase #3	$116.93	10.223%	$128.8838	$128.88	$128.90	$128.90
Purchase #4	$218.64	4.180%	$227.7792	$227.78	$227.80	$227.80
Purchase #5	$119.28	12.384%	$134.0516	$134.05	$134.05	$134.10
Purchase #6	$93.83	3.835%	$97.4284	$97.43	$97.45	$97.40
Purchase #7	$89.48	6.871%	$95.6282	$95.63	$95.65	$95.60
7 purchase totals =	$1,016.38		$1,100.4388	$1,100.44	$1,100.55	$1,100.40