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	$100.33	3.276%	$103.6168	$103.62	$103.60	$103.60
Purchase #2	$6.85	5.672%	$7.2385	$7.24	$7.25	$7.20
Purchase #3	$179.96	10.583%	$199.0052	$199.01	$199.00	$199.00
Purchase #4	$150.83	13.786%	$171.6234	$171.62	$171.60	$171.60
Purchase #5	$128.34	13.375%	$145.5055	$145.51	$145.50	$145.50
Purchase #6	$79.47	8.146%	$85.9436	$85.94	$85.95	$85.90
Purchase #7	$116.67	10.602%	$129.0394	$129.04	$129.05	$129.00
7 purchase totals =	$762.45		$841.9724	$841.98	$841.95	$841.80