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	$15.71	8.782%	$17.0897	$17.09	$17.10	$17.10
Purchase #2	$53.44	10.517%	$59.0603	$59.06	$59.05	$59.10
Purchase #3	$211.76	13.681%	$240.7309	$240.73	$240.75	$240.70
Purchase #4	$7.30	4.660%	$7.6402	$7.64	$7.65	$7.60
Purchase #5	$192.50	6.642%	$205.2859	$205.29	$205.30	$205.30
Purchase #6	$77.49	6.736%	$82.7097	$82.71	$82.70	$82.70
Purchase #7	$30.56	7.456%	$32.8386	$32.84	$32.85	$32.80
7 purchase totals =	$588.76		$645.3553	$645.36	$645.40	$645.30