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	$6.67	8.807%	$7.2574	$7.26	$7.25	$7.30
Purchase #2	$180.83	8.521%	$196.2385	$196.24	$196.25	$196.20
Purchase #3	$139.79	4.231%	$145.7045	$145.70	$145.70	$145.70
Purchase #4	$216.66	13.275%	$245.4216	$245.42	$245.40	$245.40
Purchase #5	$147.97	11.395%	$164.8312	$164.83	$164.85	$164.80
Purchase #6	$80.76	5.842%	$85.478	$85.48	$85.50	$85.50
Purchase #7	$117.99	12.444%	$132.6727	$132.67	$132.65	$132.70
7 purchase totals =	$890.67		$977.6039	$977.60	$977.60	$977.60