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	$53.54	4.287%	$55.8353	$55.84	$55.85	$55.80
Purchase #2	$168.77	7.174%	$180.8776	$180.88	$180.90	$180.90
Purchase #3	$118.94	12.872%	$134.25	$134.25	$134.25	$134.30
Purchase #4	$39.56	5.391%	$41.6927	$41.69	$41.70	$41.70
Purchase #5	$79.60	4.169%	$82.9185	$82.92	$82.90	$82.90
Purchase #6	$210.50	13.758%	$239.4606	$239.46	$239.45	$239.50
Purchase #7	$135.33	12.689%	$152.502	$152.50	$152.50	$152.50
7 purchase totals =	$806.24		$887.5367	$887.54	$887.55	$887.60