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	$187.27	13.789%	$213.0927	$213.09	$213.10	$213.10
Purchase #2	$49.65	7.361%	$53.3047	$53.30	$53.30	$53.30
Purchase #3	$84.97	4.188%	$88.5285	$88.53	$88.55	$88.50
Purchase #4	$186.29	5.308%	$196.1783	$196.18	$196.20	$196.20
Purchase #5	$50.72	9.819%	$55.7002	$55.70	$55.70	$55.70
Purchase #6	$57.59	6.621%	$61.403	$61.40	$61.40	$61.40
Purchase #7	$173.95	4.806%	$182.31	$182.31	$182.30	$182.30
7 purchase totals =	$790.44		$850.5174	$850.51	$850.55	$850.50