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	$38.69	9.722%	$42.4514	$42.45	$42.45	$42.50
Purchase #2	$246.94	4.503%	$258.0597	$258.06	$258.05	$258.10
Purchase #3	$249.74	3.648%	$258.8505	$258.85	$258.85	$258.90
Purchase #4	$210.59	12.288%	$236.4673	$236.47	$236.45	$236.50
Purchase #5	$190.34	8.653%	$206.8101	$206.81	$206.80	$206.80
Purchase #6	$104.43	4.483%	$109.1116	$109.11	$109.10	$109.10
Purchase #7	$54.43	5.500%	$57.4237	$57.42	$57.40	$57.40
7 purchase totals =	$1,095.16		$1,169.1743	$1,169.17	$1,169.10	$1,169.30