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	$112.82	12.767%	$127.2237	$127.22	$127.20	$127.20
Purchase #2	$169.85	7.747%	$183.0083	$183.01	$183.00	$183.00
Purchase #3	$130.54	11.465%	$145.5064	$145.51	$145.50	$145.50
Purchase #4	$93.73	11.542%	$104.5483	$104.55	$104.55	$104.50
Purchase #5	$68.83	5.387%	$72.5379	$72.54	$72.55	$72.50
Purchase #6	$57.55	3.621%	$59.6339	$59.63	$59.65	$59.60
Purchase #7	$133.95	7.303%	$143.7324	$143.73	$143.75	$143.70
7 purchase totals =	$767.27		$836.1909	$836.19	$836.20	$836.00