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	$82.91	10.326%	$91.4713	$91.47	$91.45	$91.50
Purchase #2	$117.84	3.304%	$121.7334	$121.73	$121.75	$121.70
Purchase #3	$93.77	12.640%	$105.6225	$105.62	$105.60	$105.60
Purchase #4	$164.44	12.623%	$185.1973	$185.20	$185.20	$185.20
Purchase #5	$119.86	6.835%	$128.0524	$128.05	$128.05	$128.10
Purchase #6	$149.66	10.730%	$165.7185	$165.72	$165.70	$165.70
Purchase #7	$40.77	7.276%	$43.7364	$43.74	$43.75	$43.70
7 purchase totals =	$769.25		$841.5318	$841.53	$841.50	$841.50