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	$37.75	6.818%	$40.3238	$40.32	$40.30	$40.30
Purchase #2	$154.27	7.317%	$165.5579	$165.56	$165.55	$165.60
Purchase #3	$119.28	12.586%	$134.2926	$134.29	$134.30	$134.30
Purchase #4	$19.37	8.484%	$21.0134	$21.01	$21.00	$21.00
Purchase #5	$18.28	8.265%	$19.7908	$19.79	$19.80	$19.80
Purchase #6	$162.58	7.840%	$175.3263	$175.33	$175.35	$175.30
Purchase #7	$47.72	7.231%	$51.1706	$51.17	$51.15	$51.20
7 purchase totals =	$559.25		$607.4754	$607.47	$607.45	$607.50