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	$109.72	10.861%	$121.6367	$121.64	$121.65	$121.60
Purchase #2	$229.64	10.636%	$254.0645	$254.06	$254.05	$254.10
Purchase #3	$99.39	12.475%	$111.7889	$111.79	$111.80	$111.80
Purchase #4	$181.88	12.122%	$203.9275	$203.93	$203.95	$203.90
Purchase #5	$146.55	5.707%	$154.9136	$154.91	$154.90	$154.90
Purchase #6	$84.27	8.662%	$91.5695	$91.57	$91.55	$91.60
Purchase #7	$177.50	4.796%	$186.0129	$186.01	$186.00	$186.00
7 purchase totals =	$1,028.95		$1,123.9136	$1,123.91	$1,123.90	$1,123.90