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	$137.27	8.710%	$149.2262	$149.23	$149.25	$149.20
Purchase #2	$53.62	5.454%	$56.5444	$56.54	$56.55	$56.50
Purchase #3	$88.47	3.141%	$91.2488	$91.25	$91.25	$91.20
Purchase #4	$76.97	7.110%	$82.4426	$82.44	$82.45	$82.40
Purchase #5	$224.37	3.128%	$231.3883	$231.39	$231.40	$231.40
Purchase #6	$48.31	12.387%	$54.2942	$54.29	$54.30	$54.30
Purchase #7	$37.29	5.669%	$39.404	$39.40	$39.40	$39.40
7 purchase totals =	$666.30		$704.5485	$704.54	$704.60	$704.40