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	$227.75	11.738%	$254.4833	$254.48	$254.50	$254.50
Purchase #2	$183.45	10.869%	$203.3892	$203.39	$203.40	$203.40
Purchase #3	$247.77	8.809%	$269.5961	$269.60	$269.60	$269.60
Purchase #4	$40.74	11.459%	$45.4084	$45.41	$45.40	$45.40
Purchase #5	$117.65	13.805%	$133.8916	$133.89	$133.90	$133.90
Purchase #6	$150.72	5.104%	$158.4127	$158.41	$158.40	$158.40
Purchase #7	$213.56	4.826%	$223.8664	$223.87	$223.85	$223.90
7 purchase totals =	$1,181.64		$1,289.0477	$1,289.05	$1,289.05	$1,289.10