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	$116.48	3.304%	$120.3285	$120.33	$120.35	$120.30
Purchase #2	$81.61	8.301%	$88.3844	$88.38	$88.40	$88.40
Purchase #3	$16.97	8.716%	$18.4491	$18.45	$18.45	$18.40
Purchase #4	$147.82	7.272%	$158.5695	$158.57	$158.55	$158.60
Purchase #5	$29.78	10.836%	$33.007	$33.01	$33.00	$33.00
Purchase #6	$46.29	3.572%	$47.9435	$47.94	$47.95	$47.90
Purchase #7	$162.66	10.397%	$179.5718	$179.57	$179.55	$179.60
7 purchase totals =	$601.61		$646.2538	$646.25	$646.25	$646.20