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	$52.50	4.848%	$55.0452	$55.05	$55.05	$55.00
Purchase #2	$238.34	11.564%	$265.9016	$265.90	$265.90	$265.90
Purchase #3	$50.31	3.140%	$51.8897	$51.89	$51.90	$51.90
Purchase #4	$133.69	4.601%	$139.8411	$139.84	$139.85	$139.80
Purchase #5	$126.52	10.512%	$139.8198	$139.82	$139.80	$139.80
Purchase #6	$215.73	11.156%	$239.7968	$239.80	$239.80	$239.80
Purchase #7	$231.58	3.107%	$238.7752	$238.78	$238.80	$238.80
7 purchase totals =	$1,048.67		$1,131.0694	$1,131.08	$1,131.10	$1,131.00