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	$63.65	10.438%	$70.2938	$70.29	$70.30	$70.30
Purchase #2	$152.95	11.713%	$170.865	$170.87	$170.85	$170.90
Purchase #3	$76.35	11.618%	$85.2203	$85.22	$85.20	$85.20
Purchase #4	$30.76	4.757%	$32.2233	$32.22	$32.20	$32.20
Purchase #5	$89.32	10.332%	$98.5485	$98.55	$98.55	$98.50
Purchase #6	$105.39	5.503%	$111.1896	$111.19	$111.20	$111.20
Purchase #7	$81.41	12.637%	$91.6978	$91.70	$91.70	$91.70
7 purchase totals =	$599.83		$660.0383	$660.04	$660.00	$660.00