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	$100.82	3.646%	$104.4959	$104.50	$104.50	$104.50
Purchase #2	$247.87	3.728%	$257.1106	$257.11	$257.10	$257.10
Purchase #3	$91.88	9.344%	$100.4653	$100.47	$100.45	$100.50
Purchase #4	$38.89	11.361%	$43.3083	$43.31	$43.30	$43.30
Purchase #5	$66.60	7.440%	$71.555	$71.56	$71.55	$71.60
Purchase #6	$194.72	7.240%	$208.8177	$208.82	$208.80	$208.80
Purchase #7	$32.40	5.712%	$34.2507	$34.25	$34.25	$34.30
7 purchase totals =	$773.18		$820.0035	$820.02	$819.95	$820.10