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	$54.44	5.164%	$57.2513	$57.25	$57.25	$57.30
Purchase #2	$231.86	4.627%	$242.5882	$242.59	$242.60	$242.60
Purchase #3	$123.26	13.119%	$139.4305	$139.43	$139.45	$139.40
Purchase #4	$170.93	13.253%	$193.5834	$193.58	$193.60	$193.60
Purchase #5	$128.92	3.605%	$133.5676	$133.57	$133.55	$133.60
Purchase #6	$164.36	12.839%	$185.4622	$185.46	$185.45	$185.50
Purchase #7	$98.39	11.794%	$109.9941	$109.99	$110.00	$110.00
7 purchase totals =	$972.16		$1,061.8773	$1,061.87	$1,061.90	$1,062.00