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	$136.51	11.836%	$152.6673	$152.67	$152.65	$152.70
Purchase #2	$13.81	8.710%	$15.0129	$15.01	$15.00	$15.00
Purchase #3	$98.61	13.146%	$111.5733	$111.57	$111.55	$111.60
Purchase #4	$124.98	8.413%	$135.4946	$135.49	$135.50	$135.50
Purchase #5	$218.67	6.644%	$233.1984	$233.20	$233.20	$233.20
Purchase #6	$119.57	6.336%	$127.146	$127.15	$127.15	$127.10
Purchase #7	$109.67	13.166%	$124.1092	$124.11	$124.10	$124.10
7 purchase totals =	$821.82		$899.2017	$899.20	$899.15	$899.20