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	$85.57	10.304%	$94.3871	$94.39	$94.40	$94.40
Purchase #2	$48.35	6.287%	$51.3898	$51.39	$51.40	$51.40
Purchase #3	$204.86	12.275%	$230.0066	$230.01	$230.00	$230.00
Purchase #4	$125.30	7.333%	$134.4882	$134.49	$134.50	$134.50
Purchase #5	$131.85	6.112%	$139.9087	$139.91	$139.90	$139.90
Purchase #6	$129.66	12.874%	$146.3524	$146.35	$146.35	$146.40
Purchase #7	$212.53	4.471%	$222.0322	$222.03	$222.05	$222.00
7 purchase totals =	$938.12		$1,018.5650	$1,018.57	$1,018.60	$1,018.60