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	$88.72	10.585%	$98.111	$98.11	$98.10	$98.10
Purchase #2	$157.92	4.401%	$164.8701	$164.87	$164.85	$164.90
Purchase #3	$177.85	11.481%	$198.269	$198.27	$198.25	$198.30
Purchase #4	$173.82	10.644%	$192.3214	$192.32	$192.30	$192.30
Purchase #5	$72.56	8.372%	$78.6347	$78.63	$78.65	$78.60
Purchase #6	$40.55	11.720%	$45.3025	$45.30	$45.30	$45.30
Purchase #7	$151.67	7.332%	$162.7904	$162.79	$162.80	$162.80
7 purchase totals =	$863.09		$940.2991	$940.29	$940.25	$940.30