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	$164.69	13.704%	$187.2591	$187.26	$187.25	$187.30
Purchase #2	$138.31	10.484%	$152.8104	$152.81	$152.80	$152.80
Purchase #3	$105.70	9.240%	$115.4667	$115.47	$115.45	$115.50
Purchase #4	$185.75	3.228%	$191.746	$191.75	$191.75	$191.70
Purchase #5	$115.86	4.255%	$120.7898	$120.79	$120.80	$120.80
Purchase #6	$114.83	4.856%	$120.4061	$120.41	$120.40	$120.40
Purchase #7	$189.59	5.769%	$200.5274	$200.53	$200.55	$200.50
7 purchase totals =	$1,014.73		$1,089.0055	$1,089.02	$1,089.00	$1,089.00