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	$121.76	9.157%	$132.9096	$132.91	$132.90	$132.90
Purchase #2	$172.83	5.578%	$182.4705	$182.47	$182.45	$182.50
Purchase #3	$124.63	12.301%	$139.9607	$139.96	$139.95	$140.00
Purchase #4	$99.52	10.391%	$109.8611	$109.86	$109.85	$109.90
Purchase #5	$120.46	6.270%	$128.0128	$128.01	$128.00	$128.00
Purchase #6	$158.41	4.310%	$165.2375	$165.24	$165.25	$165.20
Purchase #7	$109.46	12.327%	$122.9531	$122.95	$122.95	$123.00
7 purchase totals =	$907.07		$981.4053	$981.40	$981.35	$981.50