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	$38.99	9.587%	$42.728	$42.73	$42.75	$42.70
Purchase #2	$215.25	7.150%	$230.6404	$230.64	$230.65	$230.60
Purchase #3	$229.85	13.243%	$260.289	$260.29	$260.30	$260.30
Purchase #4	$79.95	12.400%	$89.8638	$89.86	$89.85	$89.90
Purchase #5	$29.53	6.304%	$31.3916	$31.39	$31.40	$31.40
Purchase #6	$131.70	13.837%	$149.9233	$149.92	$149.90	$149.90
Purchase #7	$162.42	6.658%	$173.2339	$173.23	$173.25	$173.20
7 purchase totals =	$887.69		$978.0700	$978.06	$978.10	$978.00