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	$96.68	6.777%	$103.232	$103.23	$103.25	$103.20
Purchase #2	$150.75	9.471%	$165.0275	$165.03	$165.05	$165.00
Purchase #3	$175.55	4.845%	$184.0554	$184.06	$184.05	$184.10
Purchase #4	$89.91	11.214%	$99.9925	$99.99	$100.00	$100.00
Purchase #5	$84.63	11.442%	$94.3134	$94.31	$94.30	$94.30
Purchase #6	$66.41	7.571%	$71.4379	$71.44	$71.45	$71.40
Purchase #7	$172.89	7.369%	$185.6303	$185.63	$185.65	$185.60
7 purchase totals =	$836.82		$903.6890	$903.69	$903.75	$903.60