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	$82.39	10.114%	$90.7229	$90.72	$90.70	$90.70
Purchase #2	$182.35	12.652%	$205.4209	$205.42	$205.40	$205.40
Purchase #3	$14.65	12.656%	$16.5041	$16.50	$16.50	$16.50
Purchase #4	$27.56	13.157%	$31.1861	$31.19	$31.20	$31.20
Purchase #5	$143.31	8.198%	$155.0586	$155.06	$155.05	$155.10
Purchase #6	$83.79	7.258%	$89.8715	$89.87	$89.85	$89.90
Purchase #7	$79.41	3.511%	$82.1981	$82.20	$82.20	$82.20
7 purchase totals =	$613.46		$670.9622	$670.96	$670.90	$671.00