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	$170.90	9.735%	$187.5371	$187.54	$187.55	$187.50
Purchase #2	$95.44	4.156%	$99.4065	$99.41	$99.40	$99.40
Purchase #3	$86.81	10.652%	$96.057	$96.06	$96.05	$96.10
Purchase #4	$156.41	12.237%	$175.5499	$175.55	$175.55	$175.50
Purchase #5	$71.66	8.856%	$78.0062	$78.01	$78.00	$78.00
Purchase #6	$227.88	13.576%	$258.817	$258.82	$258.80	$258.80
Purchase #7	$15.36	5.271%	$16.1696	$16.17	$16.15	$16.20
7 purchase totals =	$824.46		$911.5433	$911.56	$911.50	$911.50