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	$200.31	7.766%	$215.8661	$215.87	$215.85	$215.90
Purchase #2	$195.90	5.477%	$206.6294	$206.63	$206.65	$206.60
Purchase #3	$120.49	6.107%	$127.8483	$127.85	$127.85	$127.80
Purchase #4	$154.53	13.261%	$175.0222	$175.02	$175.00	$175.00
Purchase #5	$18.29	9.420%	$20.0129	$20.01	$20.00	$20.00
Purchase #6	$52.30	3.262%	$54.006	$54.01	$54.00	$54.00
Purchase #7	$47.30	13.782%	$53.8189	$53.82	$53.80	$53.80
7 purchase totals =	$789.12		$853.2038	$853.21	$853.15	$853.10