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	$99.96	11.418%	$111.3734	$111.37	$111.35	$111.40
Purchase #2	$78.44	10.446%	$86.6338	$86.63	$86.65	$86.60
Purchase #3	$232.92	11.802%	$260.4092	$260.41	$260.40	$260.40
Purchase #4	$89.85	12.863%	$101.4074	$101.41	$101.40	$101.40
Purchase #5	$149.45	6.441%	$159.0761	$159.08	$159.10	$159.10
Purchase #6	$220.73	9.671%	$242.0768	$242.08	$242.10	$242.10
Purchase #7	$88.31	13.355%	$100.1038	$100.10	$100.10	$100.10
7 purchase totals =	$959.66		$1,061.0805	$1,061.08	$1,061.10	$1,061.10