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	$249.35	11.229%	$277.3495	$277.35	$277.35	$277.30
Purchase #2	$133.69	10.441%	$147.6486	$147.65	$147.65	$147.60
Purchase #3	$178.29	10.273%	$196.6057	$196.61	$196.60	$196.60
Purchase #4	$58.34	9.840%	$64.0807	$64.08	$64.10	$64.10
Purchase #5	$138.53	9.282%	$151.3884	$151.39	$151.40	$151.40
Purchase #6	$84.38	6.419%	$89.7964	$89.80	$89.80	$89.80
Purchase #7	$137.27	12.789%	$154.8255	$154.83	$154.85	$154.80
7 purchase totals =	$979.85		$1,081.6948	$1,081.71	$1,081.75	$1,081.60