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	$243.91	12.498%	$274.3939	$274.39	$274.40	$274.40
Purchase #2	$243.52	13.165%	$275.5794	$275.58	$275.60	$275.60
Purchase #3	$218.46	5.870%	$231.2836	$231.28	$231.30	$231.30
Purchase #4	$41.69	12.626%	$46.9538	$46.95	$46.95	$47.00
Purchase #5	$164.77	8.219%	$178.3124	$178.31	$178.30	$178.30
Purchase #6	$137.97	10.384%	$152.2968	$152.30	$152.30	$152.30
Purchase #7	$178.71	7.233%	$191.6361	$191.64	$191.65	$191.60
7 purchase totals =	$1,229.03		$1,350.4560	$1,350.45	$1,350.50	$1,350.50