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	$99.95	7.304%	$107.2503	$107.25	$107.25	$107.30
Purchase #2	$90.89	4.222%	$94.7274	$94.73	$94.75	$94.70
Purchase #3	$107.96	8.415%	$117.0448	$117.04	$117.05	$117.00
Purchase #4	$31.43	3.722%	$32.5998	$32.60	$32.60	$32.60
Purchase #5	$138.70	12.594%	$156.1679	$156.17	$156.15	$156.20
Purchase #6	$69.40	12.839%	$78.3103	$78.31	$78.30	$78.30
Purchase #7	$154.67	7.550%	$166.3476	$166.35	$166.35	$166.30
7 purchase totals =	$693.00		$752.4481	$752.45	$752.45	$752.40