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	$99.81	3.781%	$103.5838	$103.58	$103.60	$103.60
Purchase #2	$162.31	5.564%	$171.3409	$171.34	$171.35	$171.30
Purchase #3	$75.61	7.768%	$81.4834	$81.48	$81.50	$81.50
Purchase #4	$237.99	10.508%	$262.998	$263.00	$263.00	$263.00
Purchase #5	$248.36	3.184%	$256.2678	$256.27	$256.25	$256.30
Purchase #6	$127.43	10.494%	$140.8025	$140.80	$140.80	$140.80
Purchase #7	$51.72	4.532%	$54.064	$54.06	$54.05	$54.10
7 purchase totals =	$1,003.23		$1,070.5404	$1,070.53	$1,070.55	$1,070.60