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	$14.77	7.525%	$15.8814	$15.88	$15.90	$15.90
Purchase #2	$154.65	6.411%	$164.5646	$164.56	$164.55	$164.60
Purchase #3	$223.58	4.805%	$234.323	$234.32	$234.30	$234.30
Purchase #4	$231.47	4.465%	$241.8051	$241.81	$241.80	$241.80
Purchase #5	$181.56	10.360%	$200.3696	$200.37	$200.35	$200.40
Purchase #6	$160.93	3.326%	$166.2825	$166.28	$166.30	$166.30
Purchase #7	$199.89	9.851%	$219.5812	$219.58	$219.60	$219.60
7 purchase totals =	$1,166.85		$1,242.8074	$1,242.80	$1,242.80	$1,242.90