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	$67.68	7.263%	$72.5956	$72.60	$72.60	$72.60
Purchase #2	$112.64	11.323%	$125.3942	$125.39	$125.40	$125.40
Purchase #3	$146.78	12.783%	$165.5429	$165.54	$165.55	$165.50
Purchase #4	$97.46	11.706%	$108.8687	$108.87	$108.85	$108.90
Purchase #5	$171.43	9.783%	$188.201	$188.20	$188.20	$188.20
Purchase #6	$37.26	6.151%	$39.5519	$39.55	$39.55	$39.60
Purchase #7	$61.81	9.104%	$67.4372	$67.44	$67.45	$67.40
7 purchase totals =	$695.06		$767.5915	$767.59	$767.60	$767.60