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	$37.38	10.564%	$41.3288	$41.33	$41.35	$41.30
Purchase #2	$135.72	5.676%	$143.4235	$143.42	$143.40	$143.40
Purchase #3	$190.87	3.800%	$198.1231	$198.12	$198.10	$198.10
Purchase #4	$46.63	7.344%	$50.0545	$50.05	$50.05	$50.10
Purchase #5	$39.43	7.734%	$42.4795	$42.48	$42.50	$42.50
Purchase #6	$72.31	10.636%	$80.0009	$80.00	$80.00	$80.00
Purchase #7	$233.81	3.156%	$241.189	$241.19	$241.20	$241.20
7 purchase totals =	$756.15		$796.5993	$796.59	$796.60	$796.60