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	$123.81	10.458%	$136.758	$136.76	$136.75	$136.80
Purchase #2	$103.37	9.191%	$112.8707	$112.87	$112.85	$112.90
Purchase #3	$90.58	8.810%	$98.5601	$98.56	$98.55	$98.60
Purchase #4	$131.42	9.619%	$144.0613	$144.06	$144.05	$144.10
Purchase #5	$106.61	4.107%	$110.9885	$110.99	$111.00	$111.00
Purchase #6	$40.44	3.817%	$41.9836	$41.98	$42.00	$42.00
Purchase #7	$233.65	4.467%	$244.0871	$244.09	$244.10	$244.10
7 purchase totals =	$829.88		$889.3093	$889.31	$889.30	$889.50