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	$47.52	9.626%	$52.0943	$52.09	$52.10	$52.10
Purchase #2	$34.96	3.774%	$36.2794	$36.28	$36.30	$36.30
Purchase #3	$13.37	3.610%	$13.8527	$13.85	$13.85	$13.90
Purchase #4	$236.41	11.709%	$264.0912	$264.09	$264.10	$264.10
Purchase #5	$119.28	6.576%	$127.1239	$127.12	$127.10	$127.10
Purchase #6	$67.77	7.166%	$72.6264	$72.63	$72.65	$72.60
Purchase #7	$21.39	9.376%	$23.3955	$23.40	$23.40	$23.40
7 purchase totals =	$540.70		$589.4634	$589.46	$589.50	$589.50