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	$57.29	12.539%	$64.4736	$64.47	$64.45	$64.50
Purchase #2	$51.48	7.628%	$55.4069	$55.41	$55.40	$55.40
Purchase #3	$240.85	9.453%	$263.6176	$263.62	$263.60	$263.60
Purchase #4	$91.39	12.578%	$102.885	$102.89	$102.90	$102.90
Purchase #5	$204.29	5.522%	$215.5709	$215.57	$215.55	$215.60
Purchase #6	$94.59	6.565%	$100.7998	$100.80	$100.80	$100.80
Purchase #7	$114.50	7.707%	$123.3245	$123.32	$123.30	$123.30
7 purchase totals =	$854.39		$926.0783	$926.08	$926.00	$926.10