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	$86.81	4.318%	$90.5585	$90.56	$90.55	$90.60
Purchase #2	$221.97	9.645%	$243.379	$243.38	$243.40	$243.40
Purchase #3	$95.39	5.213%	$100.3627	$100.36	$100.35	$100.40
Purchase #4	$150.80	3.169%	$155.5789	$155.58	$155.60	$155.60
Purchase #5	$121.28	4.777%	$127.0735	$127.07	$127.05	$127.10
Purchase #6	$173.42	8.637%	$188.3983	$188.40	$188.40	$188.40
Purchase #7	$78.84	3.674%	$81.7366	$81.74	$81.75	$81.70
7 purchase totals =	$928.51		$987.0875	$987.09	$987.10	$987.20