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	$54.97	4.726%	$57.5679	$57.57	$57.55	$57.60
Purchase #2	$65.48	9.366%	$71.6129	$71.61	$71.60	$71.60
Purchase #3	$112.55	13.431%	$127.6666	$127.67	$127.65	$127.70
Purchase #4	$56.27	9.358%	$61.5357	$61.54	$61.55	$61.50
Purchase #5	$66.64	13.150%	$75.4032	$75.40	$75.40	$75.40
Purchase #6	$61.53	13.572%	$69.8809	$69.88	$69.90	$69.90
Purchase #7	$130.96	13.292%	$148.3672	$148.37	$148.35	$148.40
7 purchase totals =	$548.40		$612.0344	$612.04	$612.00	$612.10