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	$133.78	10.817%	$148.251	$148.25	$148.25	$148.30
Purchase #2	$48.93	5.157%	$51.4533	$51.45	$51.45	$51.50
Purchase #3	$250.54	10.521%	$276.8993	$276.90	$276.90	$276.90
Purchase #4	$190.30	7.105%	$203.8208	$203.82	$203.80	$203.80
Purchase #5	$17.27	7.219%	$18.5167	$18.52	$18.50	$18.50
Purchase #6	$99.32	3.792%	$103.0862	$103.09	$103.10	$103.10
Purchase #7	$17.50	4.760%	$18.333	$18.33	$18.35	$18.30
7 purchase totals =	$757.64		$820.3603	$820.36	$820.35	$820.40