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	$10.88	9.207%	$11.8817	$11.88	$11.90	$11.90
Purchase #2	$126.86	10.446%	$140.1118	$140.11	$140.10	$140.10
Purchase #3	$27.82	9.511%	$30.466	$30.47	$30.45	$30.50
Purchase #4	$139.66	4.545%	$146.0075	$146.01	$146.00	$146.00
Purchase #5	$29.82	4.155%	$31.059	$31.06	$31.05	$31.10
Purchase #6	$52.96	6.849%	$56.5872	$56.59	$56.60	$56.60
Purchase #7	$36.79	12.289%	$41.3111	$41.31	$41.30	$41.30
7 purchase totals =	$424.79		$457.4243	$457.43	$457.40	$457.50