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	$238.31	12.678%	$268.5229	$268.52	$268.50	$268.50
Purchase #2	$146.38	6.785%	$156.3119	$156.31	$156.30	$156.30
Purchase #3	$61.53	7.307%	$66.026	$66.03	$66.05	$66.00
Purchase #4	$118.32	13.548%	$134.35	$134.35	$134.35	$134.40
Purchase #5	$239.33	6.744%	$255.4704	$255.47	$255.45	$255.50
Purchase #6	$85.82	6.353%	$91.2721	$91.27	$91.25	$91.30
Purchase #7	$167.61	4.652%	$175.4072	$175.41	$175.40	$175.40
7 purchase totals =	$1,057.30		$1,147.3605	$1,147.36	$1,147.30	$1,147.40