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	$105.60	3.702%	$109.5093	$109.51	$109.50	$109.50
Purchase #2	$198.95	3.218%	$205.3522	$205.35	$205.35	$205.40
Purchase #3	$166.67	9.402%	$182.3403	$182.34	$182.35	$182.30
Purchase #4	$176.86	13.292%	$200.3682	$200.37	$200.35	$200.40
Purchase #5	$139.28	7.691%	$149.992	$149.99	$150.00	$150.00
Purchase #6	$219.94	9.423%	$240.6649	$240.66	$240.65	$240.70
Purchase #7	$83.52	13.170%	$94.5196	$94.52	$94.50	$94.50
7 purchase totals =	$1,090.82		$1,182.7465	$1,182.74	$1,182.70	$1,182.80