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	$73.72	6.151%	$78.2545	$78.25	$78.25	$78.30
Purchase #2	$104.29	10.571%	$115.3145	$115.31	$115.30	$115.30
Purchase #3	$237.36	8.331%	$257.1345	$257.13	$257.15	$257.10
Purchase #4	$231.82	8.865%	$252.3708	$252.37	$252.35	$252.40
Purchase #5	$242.61	5.856%	$256.8172	$256.82	$256.80	$256.80
Purchase #6	$196.75	9.339%	$215.1245	$215.12	$215.10	$215.10
Purchase #7	$114.83	9.340%	$125.5551	$125.56	$125.55	$125.60
7 purchase totals =	$1,201.38		$1,300.5711	$1,300.56	$1,300.50	$1,300.60