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	$123.83	5.398%	$130.5143	$130.51	$130.50	$130.50
Purchase #2	$137.63	6.166%	$146.1163	$146.12	$146.10	$146.10
Purchase #3	$152.62	8.661%	$165.8384	$165.84	$165.85	$165.80
Purchase #4	$214.33	6.136%	$227.4813	$227.48	$227.50	$227.50
Purchase #5	$123.70	8.220%	$133.8681	$133.87	$133.85	$133.90
Purchase #6	$95.52	8.360%	$103.5055	$103.51	$103.50	$103.50
Purchase #7	$12.43	8.238%	$13.454	$13.45	$13.45	$13.50
7 purchase totals =	$860.06		$920.7779	$920.78	$920.75	$920.80