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	$106.98	8.449%	$116.0187	$116.02	$116.00	$116.00
Purchase #2	$222.54	12.777%	$250.9739	$250.97	$250.95	$251.00
Purchase #3	$152.38	8.650%	$165.5609	$165.56	$165.55	$165.60
Purchase #4	$109.39	9.833%	$120.1463	$120.15	$120.15	$120.10
Purchase #5	$109.96	12.420%	$123.617	$123.62	$123.60	$123.60
Purchase #6	$139.53	9.632%	$152.9695	$152.97	$152.95	$153.00
Purchase #7	$47.94	3.585%	$49.6586	$49.66	$49.65	$49.70
7 purchase totals =	$888.72		$978.9449	$978.95	$978.85	$979.00