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	$37.32	12.643%	$42.0384	$42.04	$42.05	$42.00
Purchase #2	$102.43	12.110%	$114.8343	$114.83	$114.85	$114.80
Purchase #3	$159.90	5.545%	$168.7665	$168.77	$168.75	$168.80
Purchase #4	$146.49	4.352%	$152.8652	$152.87	$152.85	$152.90
Purchase #5	$171.64	8.616%	$186.4285	$186.43	$186.45	$186.40
Purchase #6	$235.45	5.642%	$248.7341	$248.73	$248.75	$248.70
Purchase #7	$149.38	8.120%	$161.5097	$161.51	$161.50	$161.50
7 purchase totals =	$1,002.61		$1,075.1767	$1,075.18	$1,075.20	$1,075.10