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	$129.50	11.612%	$144.5375	$144.54	$144.55	$144.50
Purchase #2	$213.26	7.403%	$229.0476	$229.05	$229.05	$229.00
Purchase #3	$208.89	10.853%	$231.5608	$231.56	$231.55	$231.60
Purchase #4	$71.68	12.219%	$80.4386	$80.44	$80.45	$80.40
Purchase #5	$130.29	13.305%	$147.6251	$147.63	$147.65	$147.60
Purchase #6	$175.57	10.682%	$194.3244	$194.32	$194.30	$194.30
Purchase #7	$86.88	10.367%	$95.8868	$95.89	$95.90	$95.90
7 purchase totals =	$1,016.07		$1,123.4208	$1,123.43	$1,123.45	$1,123.30