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	$148.42	3.234%	$153.2199	$153.22	$153.20	$153.20
Purchase #2	$227.51	10.395%	$251.1597	$251.16	$251.15	$251.20
Purchase #3	$154.37	12.380%	$173.481	$173.48	$173.50	$173.50
Purchase #4	$169.82	6.319%	$180.5509	$180.55	$180.55	$180.60
Purchase #5	$128.63	6.765%	$137.3318	$137.33	$137.35	$137.30
Purchase #6	$99.64	5.826%	$105.445	$105.45	$105.45	$105.40
Purchase #7	$36.51	7.458%	$39.2329	$39.23	$39.25	$39.20
7 purchase totals =	$964.90		$1,040.4212	$1,040.42	$1,040.45	$1,040.40