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	$164.33	9.541%	$180.0087	$180.01	$180.00	$180.00
Purchase #2	$116.80	12.860%	$131.8205	$131.82	$131.80	$131.80
Purchase #3	$46.45	9.546%	$50.8841	$50.88	$50.90	$50.90
Purchase #4	$24.32	11.687%	$27.1623	$27.16	$27.15	$27.20
Purchase #5	$144.34	4.410%	$150.7054	$150.71	$150.70	$150.70
Purchase #6	$238.29	4.346%	$248.6461	$248.65	$248.65	$248.60
Purchase #7	$51.28	12.689%	$57.7869	$57.79	$57.80	$57.80
7 purchase totals =	$785.81		$847.0140	$847.02	$847.00	$847.00