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	$74.25	4.328%	$77.4635	$77.46	$77.45	$77.50
Purchase #2	$210.31	6.704%	$224.4092	$224.41	$224.40	$224.40
Purchase #3	$55.50	5.122%	$58.3427	$58.34	$58.35	$58.30
Purchase #4	$38.85	3.348%	$40.1507	$40.15	$40.15	$40.20
Purchase #5	$96.43	9.249%	$105.3488	$105.35	$105.35	$105.30
Purchase #6	$108.52	7.623%	$116.7925	$116.79	$116.80	$116.80
Purchase #7	$42.40	3.183%	$43.7496	$43.75	$43.75	$43.70
7 purchase totals =	$626.26		$666.2570	$666.25	$666.25	$666.20