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	$237.56	3.291%	$245.3781	$245.38	$245.40	$245.40
Purchase #2	$79.34	13.302%	$89.8938	$89.89	$89.90	$89.90
Purchase #3	$41.88	5.843%	$44.327	$44.33	$44.35	$44.30
Purchase #4	$164.79	10.635%	$182.3154	$182.32	$182.30	$182.30
Purchase #5	$127.27	12.520%	$143.2042	$143.20	$143.20	$143.20
Purchase #6	$19.51	9.300%	$21.3244	$21.32	$21.30	$21.30
Purchase #7	$196.32	9.733%	$215.4278	$215.43	$215.45	$215.40
7 purchase totals =	$866.67		$941.8707	$941.87	$941.90	$941.80