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	$45.59	7.618%	$49.063	$49.06	$49.05	$49.10
Purchase #2	$34.84	8.283%	$37.7258	$37.73	$37.75	$37.70
Purchase #3	$112.27	13.783%	$127.7442	$127.74	$127.75	$127.70
Purchase #4	$40.40	6.617%	$43.0733	$43.07	$43.05	$43.10
Purchase #5	$149.60	9.711%	$164.1277	$164.13	$164.15	$164.10
Purchase #6	$61.37	9.732%	$67.3425	$67.34	$67.35	$67.30
Purchase #7	$104.60	3.829%	$108.6051	$108.61	$108.60	$108.60
7 purchase totals =	$548.67		$597.6816	$597.68	$597.70	$597.60