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	$50.33	8.713%	$54.7153	$54.72	$54.70	$54.70
Purchase #2	$55.80	6.153%	$59.2334	$59.23	$59.25	$59.20
Purchase #3	$103.41	7.835%	$111.5122	$111.51	$111.50	$111.50
Purchase #4	$189.64	7.661%	$204.1683	$204.17	$204.15	$204.20
Purchase #5	$94.37	10.280%	$104.0712	$104.07	$104.05	$104.10
Purchase #6	$85.42	10.782%	$94.63	$94.63	$94.65	$94.60
Purchase #7	$174.30	8.125%	$188.4619	$188.46	$188.45	$188.50
7 purchase totals =	$753.27		$816.7923	$816.79	$816.75	$816.80