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	$233.61	8.471%	$253.3991	$253.40	$253.40	$253.40
Purchase #2	$114.31	3.584%	$118.4069	$118.41	$118.40	$118.40
Purchase #3	$153.96	7.687%	$165.7949	$165.79	$165.80	$165.80
Purchase #4	$245.29	4.681%	$256.772	$256.77	$256.75	$256.80
Purchase #5	$121.79	11.858%	$136.2319	$136.23	$136.25	$136.20
Purchase #6	$97.25	7.323%	$104.3716	$104.37	$104.35	$104.40
Purchase #7	$100.50	5.374%	$105.9009	$105.90	$105.90	$105.90
7 purchase totals =	$1,066.71		$1,140.8773	$1,140.87	$1,140.85	$1,140.90