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	$164.43	12.242%	$184.5595	$184.56	$184.55	$184.60
Purchase #2	$92.33	7.698%	$99.4376	$99.44	$99.45	$99.40
Purchase #3	$170.88	5.811%	$180.8098	$180.81	$180.80	$180.80
Purchase #4	$43.82	9.340%	$47.9128	$47.91	$47.90	$47.90
Purchase #5	$52.44	13.707%	$59.628	$59.63	$59.65	$59.60
Purchase #6	$19.81	7.312%	$21.2585	$21.26	$21.25	$21.30
Purchase #7	$65.29	8.226%	$70.6608	$70.66	$70.65	$70.70
7 purchase totals =	$609.00		$664.2670	$664.27	$664.25	$664.30