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	$65.70	3.153%	$67.7715	$67.77	$67.75	$67.80
Purchase #2	$173.30	3.757%	$179.8109	$179.81	$179.80	$179.80
Purchase #3	$5.89	10.746%	$6.5229	$6.52	$6.50	$6.50
Purchase #4	$58.78	12.547%	$66.1551	$66.16	$66.15	$66.20
Purchase #5	$73.51	12.757%	$82.8877	$82.89	$82.90	$82.90
Purchase #6	$129.55	9.610%	$141.9998	$142.00	$142.00	$142.00
Purchase #7	$246.80	13.394%	$279.8564	$279.86	$279.85	$279.90
7 purchase totals =	$753.53		$825.0043	$825.01	$824.95	$825.10