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	$17.36	7.252%	$18.6189	$18.62	$18.60	$18.60
Purchase #2	$103.94	5.792%	$109.9602	$109.96	$109.95	$110.00
Purchase #3	$233.51	7.797%	$251.7168	$251.72	$251.70	$251.70
Purchase #4	$75.33	4.357%	$78.6121	$78.61	$78.60	$78.60
Purchase #5	$69.35	3.229%	$71.5893	$71.59	$71.60	$71.60
Purchase #6	$170.96	4.327%	$178.3574	$178.36	$178.35	$178.40
Purchase #7	$242.31	10.693%	$268.2202	$268.22	$268.20	$268.20
7 purchase totals =	$912.76		$977.0749	$977.08	$977.00	$977.10