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	$231.69	3.395%	$239.5559	$239.56	$239.55	$239.60
Purchase #2	$179.41	11.824%	$200.6234	$200.62	$200.60	$200.60
Purchase #3	$223.63	7.546%	$240.5051	$240.51	$240.50	$240.50
Purchase #4	$44.52	9.176%	$48.6052	$48.61	$48.60	$48.60
Purchase #5	$89.46	6.483%	$95.2597	$95.26	$95.25	$95.30
Purchase #6	$212.37	13.865%	$241.8151	$241.82	$241.80	$241.80
Purchase #7	$189.44	12.751%	$213.5955	$213.60	$213.60	$213.60
7 purchase totals =	$1,170.52		$1,279.9599	$1,279.98	$1,279.90	$1,280.00