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	$79.68	12.803%	$89.8814	$89.88	$89.90	$89.90
Purchase #2	$167.33	4.722%	$175.2313	$175.23	$175.25	$175.20
Purchase #3	$93.39	11.210%	$103.859	$103.86	$103.85	$103.90
Purchase #4	$27.64	10.123%	$30.438	$30.44	$30.45	$30.40
Purchase #5	$214.38	11.132%	$238.2448	$238.24	$238.25	$238.20
Purchase #6	$207.93	13.395%	$235.7822	$235.78	$235.80	$235.80
Purchase #7	$97.96	5.154%	$103.0089	$103.01	$103.00	$103.00
7 purchase totals =	$888.31		$976.4456	$976.44	$976.50	$976.40