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	$184.98	7.242%	$198.3763	$198.38	$198.40	$198.40
Purchase #2	$135.82	5.392%	$143.1434	$143.14	$143.15	$143.10
Purchase #3	$99.98	11.396%	$111.3737	$111.37	$111.35	$111.40
Purchase #4	$97.25	12.716%	$109.6163	$109.62	$109.60	$109.60
Purchase #5	$39.35	6.835%	$42.0396	$42.04	$42.05	$42.00
Purchase #6	$144.61	10.280%	$159.4759	$159.48	$159.50	$159.50
Purchase #7	$61.75	10.531%	$68.2529	$68.25	$68.25	$68.30
7 purchase totals =	$763.74		$832.2781	$832.28	$832.30	$832.30