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	$173.28	13.575%	$196.8028	$196.80	$196.80	$196.80
Purchase #2	$230.41	5.804%	$243.783	$243.78	$243.80	$243.80
Purchase #3	$27.70	8.649%	$30.0958	$30.10	$30.10	$30.10
Purchase #4	$229.71	13.871%	$261.5731	$261.57	$261.55	$261.60
Purchase #5	$50.62	13.708%	$57.559	$57.56	$57.55	$57.60
Purchase #6	$231.69	7.749%	$249.6437	$249.64	$249.65	$249.60
Purchase #7	$57.40	6.374%	$61.0587	$61.06	$61.05	$61.10
7 purchase totals =	$1,000.81		$1,100.5161	$1,100.51	$1,100.50	$1,100.60