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	$70.35	11.738%	$78.6077	$78.61	$78.60	$78.60
Purchase #2	$199.55	9.531%	$218.5691	$218.57	$218.55	$218.60
Purchase #3	$101.79	10.850%	$112.8342	$112.83	$112.85	$112.80
Purchase #4	$170.27	11.590%	$190.0043	$190.00	$190.00	$190.00
Purchase #5	$174.72	6.555%	$186.1729	$186.17	$186.15	$186.20
Purchase #6	$114.98	10.364%	$126.8965	$126.90	$126.90	$126.90
Purchase #7	$173.76	10.479%	$191.9683	$191.97	$191.95	$192.00
7 purchase totals =	$1,005.42		$1,105.0530	$1,105.05	$1,105.00	$1,105.10