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	$28.60	4.295%	$29.8284	$29.83	$29.85	$29.80
Purchase #2	$200.92	11.774%	$224.5763	$224.58	$224.60	$224.60
Purchase #3	$240.52	13.606%	$273.2452	$273.25	$273.25	$273.20
Purchase #4	$21.83	12.715%	$24.6057	$24.61	$24.60	$24.60
Purchase #5	$49.53	13.694%	$56.3126	$56.31	$56.30	$56.30
Purchase #6	$173.30	9.589%	$189.9177	$189.92	$189.90	$189.90
Purchase #7	$191.26	11.834%	$213.8937	$213.89	$213.90	$213.90
7 purchase totals =	$905.96		$1,012.3796	$1,012.39	$1,012.40	$1,012.30