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	$231.41	4.280%	$241.3143	$241.31	$241.30	$241.30
Purchase #2	$166.78	12.109%	$186.9754	$186.98	$187.00	$187.00
Purchase #3	$73.35	11.118%	$81.5051	$81.51	$81.50	$81.50
Purchase #4	$222.36	9.211%	$242.8416	$242.84	$242.85	$242.80
Purchase #5	$99.69	5.515%	$105.1879	$105.19	$105.20	$105.20
Purchase #6	$118.56	6.643%	$126.4359	$126.44	$126.45	$126.40
Purchase #7	$29.65	7.278%	$31.8079	$31.81	$31.80	$31.80
7 purchase totals =	$941.80		$1,016.0681	$1,016.08	$1,016.10	$1,016.00