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	$220.94	8.837%	$240.4645	$240.46	$240.45	$240.50
Purchase #2	$99.59	10.611%	$110.1575	$110.16	$110.15	$110.20
Purchase #3	$10.55	5.385%	$11.1181	$11.12	$11.10	$11.10
Purchase #4	$202.52	9.345%	$221.4455	$221.45	$221.45	$221.40
Purchase #5	$216.96	5.378%	$228.6281	$228.63	$228.65	$228.60
Purchase #6	$203.54	4.187%	$212.0622	$212.06	$212.05	$212.10
Purchase #7	$55.59	7.263%	$59.6275	$59.63	$59.65	$59.60
7 purchase totals =	$1,009.69		$1,083.5034	$1,083.51	$1,083.50	$1,083.50