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	$189.46	9.162%	$206.8183	$206.82	$206.80	$206.80
Purchase #2	$116.75	5.455%	$123.1187	$123.12	$123.10	$123.10
Purchase #3	$99.38	12.133%	$111.4378	$111.44	$111.45	$111.40
Purchase #4	$195.90	13.550%	$222.4445	$222.44	$222.45	$222.40
Purchase #5	$142.53	8.240%	$154.2745	$154.27	$154.25	$154.30
Purchase #6	$90.30	3.455%	$93.4199	$93.42	$93.40	$93.40
Purchase #7	$193.39	12.395%	$217.3607	$217.36	$217.35	$217.40
7 purchase totals =	$1,027.71		$1,128.8744	$1,128.87	$1,128.80	$1,128.80