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	$134.44	12.762%	$151.5972	$151.60	$151.60	$151.60
Purchase #2	$96.32	3.297%	$99.4957	$99.50	$99.50	$99.50
Purchase #3	$57.59	10.170%	$63.4469	$63.45	$63.45	$63.40
Purchase #4	$144.65	10.519%	$159.8657	$159.87	$159.85	$159.90
Purchase #5	$131.83	10.265%	$145.3623	$145.36	$145.35	$145.40
Purchase #6	$215.73	8.754%	$234.615	$234.62	$234.60	$234.60
Purchase #7	$142.89	11.279%	$159.0066	$159.01	$159.00	$159.00
7 purchase totals =	$923.45		$1,013.3894	$1,013.41	$1,013.35	$1,013.40