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	$114.85	9.503%	$125.7642	$125.76	$125.75	$125.80
Purchase #2	$113.64	5.858%	$120.297	$120.30	$120.30	$120.30
Purchase #3	$176.80	13.590%	$200.8271	$200.83	$200.85	$200.80
Purchase #4	$38.59	6.138%	$40.9587	$40.96	$40.95	$41.00
Purchase #5	$6.84	4.390%	$7.1403	$7.14	$7.15	$7.10
Purchase #6	$30.90	13.671%	$35.1243	$35.12	$35.10	$35.10
Purchase #7	$97.38	12.247%	$109.3061	$109.31	$109.30	$109.30
7 purchase totals =	$579.00		$639.4177	$639.42	$639.40	$639.40