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	$161.72	3.579%	$167.508	$167.51	$167.50	$167.50
Purchase #2	$235.38	12.776%	$265.4521	$265.45	$265.45	$265.50
Purchase #3	$132.96	5.736%	$140.5866	$140.59	$140.60	$140.60
Purchase #4	$144.93	10.478%	$160.1158	$160.12	$160.10	$160.10
Purchase #5	$79.63	12.269%	$89.3998	$89.40	$89.40	$89.40
Purchase #6	$76.75	5.689%	$81.1163	$81.12	$81.10	$81.10
Purchase #7	$224.39	6.375%	$238.6949	$238.69	$238.70	$238.70
7 purchase totals =	$1,055.76		$1,142.8735	$1,142.88	$1,142.85	$1,142.90