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	$158.87	8.790%	$172.8347	$172.83	$172.85	$172.80
Purchase #2	$74.60	10.515%	$82.4442	$82.44	$82.45	$82.40
Purchase #3	$131.66	4.636%	$137.7638	$137.76	$137.75	$137.80
Purchase #4	$200.45	9.528%	$219.5489	$219.55	$219.55	$219.50
Purchase #5	$119.93	13.563%	$136.1961	$136.20	$136.20	$136.20
Purchase #6	$165.39	13.779%	$188.1791	$188.18	$188.20	$188.20
Purchase #7	$28.91	10.345%	$31.9007	$31.90	$31.90	$31.90
7 purchase totals =	$879.81		$968.8675	$968.86	$968.90	$968.80