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	$129.41	9.538%	$141.7531	$141.75	$141.75	$141.80
Purchase #2	$119.50	4.521%	$124.9026	$124.90	$124.90	$124.90
Purchase #3	$103.58	7.603%	$111.4552	$111.46	$111.45	$111.50
Purchase #4	$232.37	13.288%	$263.2473	$263.25	$263.25	$263.20
Purchase #5	$80.67	4.860%	$84.5906	$84.59	$84.60	$84.60
Purchase #6	$48.59	4.119%	$50.5914	$50.59	$50.60	$50.60
Purchase #7	$143.56	11.547%	$160.1369	$160.14	$160.15	$160.10
7 purchase totals =	$857.68		$936.6771	$936.68	$936.70	$936.70