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	$62.41	4.631%	$65.3002	$65.30	$65.30	$65.30
Purchase #2	$99.57	5.257%	$104.8044	$104.80	$104.80	$104.80
Purchase #3	$217.93	5.654%	$230.2518	$230.25	$230.25	$230.30
Purchase #4	$112.29	6.231%	$119.2868	$119.29	$119.30	$119.30
Purchase #5	$132.45	8.270%	$143.4036	$143.40	$143.40	$143.40
Purchase #6	$98.38	13.770%	$111.9269	$111.93	$111.95	$111.90
Purchase #7	$209.30	4.594%	$218.9152	$218.92	$218.90	$218.90
7 purchase totals =	$932.33		$993.8889	$993.89	$993.90	$993.90