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	$100.59	11.766%	$112.4254	$112.43	$112.45	$112.40
Purchase #2	$190.56	12.771%	$214.8964	$214.90	$214.90	$214.90
Purchase #3	$73.80	11.805%	$82.5121	$82.51	$82.50	$82.50
Purchase #4	$234.91	7.187%	$251.793	$251.79	$251.80	$251.80
Purchase #5	$94.51	11.179%	$105.0753	$105.08	$105.10	$105.10
Purchase #6	$38.90	4.651%	$40.7092	$40.71	$40.70	$40.70
Purchase #7	$116.53	5.392%	$122.8133	$122.81	$122.80	$122.80
7 purchase totals =	$849.80		$930.2247	$930.23	$930.25	$930.20