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	$237.69	6.250%	$252.5456	$252.55	$252.55	$252.50
Purchase #2	$53.55	9.400%	$58.5837	$58.58	$58.60	$58.60
Purchase #3	$222.25	9.340%	$243.0082	$243.01	$243.00	$243.00
Purchase #4	$119.86	11.153%	$133.228	$133.23	$133.25	$133.20
Purchase #5	$249.28	12.165%	$279.6049	$279.60	$279.60	$279.60
Purchase #6	$73.54	11.643%	$82.1023	$82.10	$82.10	$82.10
Purchase #7	$134.68	12.118%	$151.0005	$151.00	$151.00	$151.00
7 purchase totals =	$1,090.85		$1,200.0732	$1,200.07	$1,200.10	$1,200.00