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	$118.67	10.763%	$131.4425	$131.44	$131.45	$131.40
Purchase #2	$69.30	13.147%	$78.4109	$78.41	$78.40	$78.40
Purchase #3	$128.90	10.854%	$142.8908	$142.89	$142.90	$142.90
Purchase #4	$147.48	9.377%	$161.3092	$161.31	$161.30	$161.30
Purchase #5	$191.35	6.551%	$203.8853	$203.89	$203.90	$203.90
Purchase #6	$223.38	4.335%	$233.0635	$233.06	$233.05	$233.10
Purchase #7	$111.52	13.871%	$126.9889	$126.99	$127.00	$127.00
7 purchase totals =	$990.60		$1,077.9911	$1,077.99	$1,078.00	$1,078.00