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	$36.42	11.201%	$40.4994	$40.50	$40.50	$40.50
Purchase #2	$161.63	4.218%	$168.4476	$168.45	$168.45	$168.40
Purchase #3	$245.68	13.475%	$278.7854	$278.79	$278.80	$278.80
Purchase #4	$184.95	13.534%	$209.9811	$209.98	$210.00	$210.00
Purchase #5	$64.82	4.135%	$67.5003	$67.50	$67.50	$67.50
Purchase #6	$129.80	9.641%	$142.314	$142.31	$142.30	$142.30
Purchase #7	$70.90	12.704%	$79.9071	$79.91	$79.90	$79.90
7 purchase totals =	$894.20		$987.4349	$987.44	$987.45	$987.40