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	$120.40	5.562%	$127.0966	$127.10	$127.10	$127.10
Purchase #2	$224.43	9.713%	$246.2289	$246.23	$246.25	$246.20
Purchase #3	$114.50	4.323%	$119.4498	$119.45	$119.45	$119.40
Purchase #4	$86.27	13.780%	$98.158	$98.16	$98.15	$98.20
Purchase #5	$30.83	4.757%	$32.2966	$32.30	$32.30	$32.30
Purchase #6	$138.60	13.572%	$157.4108	$157.41	$157.40	$157.40
Purchase #7	$144.73	4.221%	$150.8391	$150.84	$150.85	$150.80
7 purchase totals =	$859.76		$931.4798	$931.49	$931.50	$931.40