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	$26.73	12.229%	$29.9988	$30.00	$30.00	$30.00
Purchase #2	$242.35	9.286%	$264.8546	$264.85	$264.85	$264.90
Purchase #3	$78.79	9.818%	$86.5256	$86.53	$86.55	$86.50
Purchase #4	$229.90	11.584%	$256.5316	$256.53	$256.55	$256.50
Purchase #5	$67.82	7.205%	$72.7064	$72.71	$72.70	$72.70
Purchase #6	$226.45	12.627%	$255.0438	$255.04	$255.05	$255.00
Purchase #7	$104.70	4.565%	$109.4796	$109.48	$109.50	$109.50
7 purchase totals =	$976.74		$1,075.1404	$1,075.14	$1,075.20	$1,075.10