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	$220.40	6.549%	$234.834	$234.83	$234.85	$234.80
Purchase #2	$78.89	12.113%	$88.4459	$88.45	$88.45	$88.40
Purchase #3	$12.34	10.762%	$13.668	$13.67	$13.65	$13.70
Purchase #4	$178.28	12.330%	$200.2619	$200.26	$200.25	$200.30
Purchase #5	$149.72	4.747%	$156.8272	$156.83	$156.85	$156.80
Purchase #6	$67.71	7.136%	$72.5418	$72.54	$72.55	$72.50
Purchase #7	$133.51	11.199%	$148.4618	$148.46	$148.45	$148.50
7 purchase totals =	$840.85		$915.0406	$915.04	$915.05	$915.00