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	$109.60	12.669%	$123.4852	$123.49	$123.50	$123.50
Purchase #2	$207.54	9.580%	$227.4223	$227.42	$227.40	$227.40
Purchase #3	$134.74	11.771%	$150.6002	$150.60	$150.60	$150.60
Purchase #4	$141.78	11.844%	$158.5724	$158.57	$158.55	$158.60
Purchase #5	$89.62	11.811%	$100.205	$100.21	$100.20	$100.20
Purchase #6	$191.72	11.850%	$214.4388	$214.44	$214.45	$214.40
Purchase #7	$79.30	3.553%	$82.1175	$82.12	$82.10	$82.10
7 purchase totals =	$954.30		$1,056.8414	$1,056.85	$1,056.80	$1,056.80