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	$71.81	9.314%	$78.4984	$78.50	$78.50	$78.50
Purchase #2	$61.63	12.670%	$69.4385	$69.44	$69.45	$69.40
Purchase #3	$174.52	9.356%	$190.8481	$190.85	$190.85	$190.80
Purchase #4	$80.61	3.473%	$83.4096	$83.41	$83.40	$83.40
Purchase #5	$36.46	10.670%	$40.3503	$40.35	$40.35	$40.40
Purchase #6	$123.42	6.274%	$131.1634	$131.16	$131.15	$131.20
Purchase #7	$95.48	11.321%	$106.2893	$106.29	$106.30	$106.30
7 purchase totals =	$643.93		$699.9976	$700.00	$700.00	$700.00