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	$79.26	9.163%	$86.5226	$86.52	$86.50	$86.50
Purchase #2	$219.39	3.870%	$227.8804	$227.88	$227.90	$227.90
Purchase #3	$178.62	13.863%	$203.3821	$203.38	$203.40	$203.40
Purchase #4	$109.73	12.664%	$123.6262	$123.63	$123.65	$123.60
Purchase #5	$27.70	3.165%	$28.5767	$28.58	$28.60	$28.60
Purchase #6	$55.97	6.169%	$59.4228	$59.42	$59.40	$59.40
Purchase #7	$11.30	5.186%	$11.886	$11.89	$11.90	$11.90
7 purchase totals =	$681.97		$741.2968	$741.30	$741.35	$741.30