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	$36.89	3.623%	$38.2265	$38.23	$38.25	$38.20
Purchase #2	$138.98	7.397%	$149.2604	$149.26	$149.25	$149.30
Purchase #3	$76.98	7.396%	$82.6734	$82.67	$82.65	$82.70
Purchase #4	$135.63	9.225%	$148.1419	$148.14	$148.15	$148.10
Purchase #5	$37.32	13.444%	$42.3373	$42.34	$42.35	$42.30
Purchase #6	$144.45	10.511%	$159.6331	$159.63	$159.65	$159.60
Purchase #7	$55.27	8.458%	$59.9447	$59.94	$59.95	$59.90
7 purchase totals =	$625.52		$680.2173	$680.21	$680.25	$680.10