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	$144.91	9.360%	$158.4736	$158.47	$158.45	$158.50
Purchase #2	$102.60	6.444%	$109.2115	$109.21	$109.20	$109.20
Purchase #3	$111.70	10.398%	$123.3146	$123.31	$123.30	$123.30
Purchase #4	$220.78	10.181%	$243.2576	$243.26	$243.25	$243.30
Purchase #5	$28.36	10.820%	$31.4286	$31.43	$31.45	$31.40
Purchase #6	$157.60	7.355%	$169.1915	$169.19	$169.20	$169.20
Purchase #7	$203.77	8.642%	$221.3798	$221.38	$221.40	$221.40
7 purchase totals =	$969.72		$1,056.2572	$1,056.25	$1,056.25	$1,056.30