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	$79.54	6.253%	$84.5136	$84.51	$84.50	$84.50
Purchase #2	$86.38	4.679%	$90.4217	$90.42	$90.40	$90.40
Purchase #3	$124.97	13.140%	$141.3911	$141.39	$141.40	$141.40
Purchase #4	$204.87	4.697%	$214.4927	$214.49	$214.50	$214.50
Purchase #5	$171.43	7.587%	$184.4364	$184.44	$184.45	$184.40
Purchase #6	$237.25	4.803%	$248.6451	$248.65	$248.65	$248.60
Purchase #7	$196.42	8.215%	$212.5559	$212.56	$212.55	$212.60
7 purchase totals =	$1,100.86		$1,176.4565	$1,176.46	$1,176.45	$1,176.40