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	$49.64	11.828%	$55.5114	$55.51	$55.50	$55.50
Purchase #2	$143.87	11.820%	$160.8754	$160.88	$160.90	$160.90
Purchase #3	$48.55	11.248%	$54.0109	$54.01	$54.00	$54.00
Purchase #4	$203.56	6.773%	$217.3471	$217.35	$217.35	$217.30
Purchase #5	$235.56	5.513%	$248.5464	$248.55	$248.55	$248.50
Purchase #6	$71.94	7.624%	$77.4247	$77.42	$77.40	$77.40
Purchase #7	$174.53	5.328%	$183.829	$183.83	$183.85	$183.80
7 purchase totals =	$927.65		$997.5449	$997.55	$997.55	$997.40