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	$70.41	10.806%	$78.0185	$78.02	$78.00	$78.00
Purchase #2	$226.29	3.722%	$234.7125	$234.71	$234.70	$234.70
Purchase #3	$170.56	5.748%	$180.3638	$180.36	$180.35	$180.40
Purchase #4	$234.27	13.471%	$265.8285	$265.83	$265.85	$265.80
Purchase #5	$167.53	9.531%	$183.4973	$183.50	$183.50	$183.50
Purchase #6	$100.38	13.608%	$114.0397	$114.04	$114.05	$114.00
Purchase #7	$90.92	3.278%	$93.9004	$93.90	$93.90	$93.90
7 purchase totals =	$1,060.36		$1,150.3607	$1,150.36	$1,150.35	$1,150.30